This mod -like every other alchemy refilling mod- makes the alchemy refilling mechanic both more expensive and more involved in order to try and make it a more meaningful and enjoyable gameplay mechanic for players who prefer that to the vanilla game's passive/virtually free automated refilling mechanic.

Unlike most other alchemy refilling mods it also tries to preserve as much of the original game as possible, changing only what's needed.

That means preserving the idea that the first time you craft an alchemy item you're effectively gaining a kind of permanent character upgrade -with no downsides. This effectively made the "unlocking"  of progressively better alchemy items a character progression goal in and of itself in the vanilla game.

It also means not only preserving the way the vanilla alchemy recipes progressed in the effects they provide the player with but also the other aspects of their progression such as the amount of charges produced on a craft/refill as well as the ingredients required to craft them. The progressively larger amount of charges you got on an alchemy item also made them more useful for increasingly lengthier and tougher contract fights. The vanilla recipe lists of ingredients where a specific part or rare ingredient is needed for a specific recipe acted both as a way to prevent the player from acquiring too powerful an alchemy item too soon as well as to engage him in some meaningful rather than random/unintended monster hunting. A player's first encounter with a tough poisonous monster wouldn't be all that interesting if poison's already healing him thanks to a prematurely-obtained superior golden oriole. The act of first crafting/unlocking a recipe isn't all that meaningful if you already acquired all the ingredients incidentally, rather than actively having to hunt for them.

IMO that is lost when unlocking higher level alchemy items also brings disadvantages (higher refill costs) rather than being strictly beneficial to your character and when you take a crafting system made for a 100 hour-long open world game with over 120 recipes and replace it with one made with 30 recipes and a linear 50 hour game in mind.

Just about everything the mod does can be configured or turned off:

Simple Alchemy Refill: On/Off
^Whether or not the mod is active
(Default: on)

Meditation Automatic Refill: Off/Simple Alchemy Refill/Vanilla
^Whether automatic refilling of alchemy items during meditation is disable, set to use the apropriate ingredients for the types of items and their levels, or to be as cheap as vanilla (Default: Simple Alchemy Refill)

Meditation Automatic Refill Repeats: On/off
^Whether or not an automatic refill repeats until your items are full (in case you're using increase max quantity multipliers)
(Default: on)

Meditation Refill Requires Campfire
^Whether you need to be near a campfire for meditation automatic refill to work
(Default: On)

Alchemy Menu Cooking Requires Campfire
^Whether you need to be near a campfire for alchemy menu brewing to work
(Default: Off)

Bomb/Potion/Mutagen Potion/Oil Refill Mode: Base / Base+ Herbs /Full Recipe
^Whether refilling those items requires their formula's corresponding alchemical base, base+herbs, full recipe (no mutagens).
(Default: Refill with corresponding Base as that likely already feels expensive enough when used with my loot-reducing mods. If you're using vanilla loot lists/economy you may want to go with Corresponding Base+ Corresponding Herbs.)

Bomb/Potion/Mutagen Potion/Oil Quantity max multiplier: 1-10
^1x = no change, 2x you can stack twice as many charges of an alchemy item as before  (how much you get per refill is unchanged) etc.
(Default: 1)

Oil Refill: On/Off
^whether or not oils require refilling. Off= infinite oil same as vanilla.
(Default: On)

Oil lv1/2/3 refill quantity: 1-10
^How much oil you get when you refill an oil. Default oil refill quantity= oil level.
(Default: basic = 1, enhanced = 2, superior= 3)

Add missing recipes: on/off
^Whether or not the game automatically adds missing recipes for alchemy items you already have (added during loading).
(Default = on as both New Game and the HoS/B&W-only starts have omissions and start you off with alchemy items you don't have the recipe for (ex:Tawny owl) but that you're expected to be able to refill from the start anyway and you can only refill an item from the alchemy menu if you first have its recipe)

First you gotta locate your The Witcher 3 game install location. Usually it's somewhere like "C:\GOG Games\The Witcher 3 Wild Hunt GOTY" for Good Old Games versions of the game or "C:\Program Files (x86)\Steam\steamapps\common\The Witcher 3" for Steam versions of the game.

Mandatory:
Script Merger
Download, run/install it, run what it installed to be sure it's working.

Optional but highly recommended:
TW3 Mod Manager
Download, run/install it, run what it installed to be sure it's working. Installing it all to some place like C:\TW3Modding\ should work.
Download, run/install it, run what it installed to be sure it's working
Enable the Debug Console: https://www.nexusmods.com/witcher3/mods/3375. Press the keys on your keyboard until you figure out which one activates the console.



After that you can install most mods by downloading them manually (VORTEX NOT RECOMMENDED WITH TW3 MODS, IT WILL EVENTUALLY CAUSE PROBLEMS). Extract their contents somewhere (rightclick on the downloaded mod file->extract) and then place their files&folders in the right places in your game install yourself OR let TW3 Mod Manager extract and place them correctly for you (Recommended).

If you're not using TW3 Mod Manager you need to make sure all of your mod's \modxxx folders end up directly inside your <TW3 game install>\Mods folder (or <TW3 game install>\mods, wherever your other mods are). If there's no mods folder in your TW3 game install folder (TW3MM would've created one for you) you can create one by rightclicking on some empty space there -> "New" -> "Folder" and write Mods as its name. That means your \modxxx folders ends up as <TW3 game install>\Mods\modxxx. TW3MM would place it there automatically for you so you wouldn't have to.

If your mod has \dlcxxx folders they similarly need to be directly inside your <TW3 game install>\dlc folder (or <TW3 game install>\DLC wherever your other dlcs are). They should end up as <TW3 game install>\dlc\dlcxxx ( never <TW3 game install>\dlc\dlc\dlcxxx !). TW3MM would do this automatically for you.

Your mod's mod menu file xxx.xml would have to end up as <TW3 game install>\bin\config\r4game\user_config_matrix\pc\xxx.xml. Again, TW3MM would do this automatically for you. If you happen to have more mod menus tham what can fit on the mod menu list you can easily edit & group mod menus together into subgroups yourself using something like notepad++, example: 1-> 2 (that mod menu was placed in a "combat" subgroup, example from Menu Strings).

If your mod has custom keybinds you probably have to add them to your <My Documents>\The Witcher 3\input.settings file using some editor like notepad++. Once more, TW3MM will usually do this automatically for you.

After your mod's files & folders are in the right places you need to run patched Script Merger and merge any conflicting files that can be merged together (that means both .ws scripts and .xml bundled files).

Sadly, not all mods will automatically merge together, most probably won't (though all LEGO merge automatically with each other, obviously), but some unresolved conflicts can be solved with a little manual help:



The bottom half is the output/result of your merge, the yellow <Merge Conflict> line is the conflicting line that SM can't figure out automatically. 
Right click on the merge conflict and you get some simple options:


^There you picked the line from mod 2, but you can also pick the lines from both mods, in any order:


Or you can even write your own code in there. Of course knowing which lines to choose or how to make them work together does require you to somewhat understand what the code does. When in doubt you might try asking the concerned mod's authors & users for help in the comments sections.

However keep in mind that there's no guarantee that any 2 mods can be effectively merged together, nor is there any guarantee that 2 mods are working well together even if they merged automatically and the game seems to be running ok.

That's why to be extra safe you should carefully read each mod's install instructions to make sure there aren't any special instructions or requirements for the mod to work (some mods might require other mods to work such as the unification/community patch or shared imports) or incompatibilities, and then merge & run the game after each new mod install to make sure it's running well.

\content\scripts\game\components\inventoryComponent.ws
\content\scripts\game\gameplay\alchemy\alchemyManager.ws
\content\scripts\game\player\playerWitcher.ws
\content\scripts\game\player\r4Player.ws
\content\scripts\game\gui\menus\inventoryMenu.ws
\content\scripts\game\gui\menus\alchemyMenu.ws
\content\scripts\game\gui\_old\components\guiBaseInventoryComponent.ws
\content\scripts\game\gui\_old\components\guiPlayerInventoryComponent.ws
\content\scripts\game\gui\_old\components\guiTooltipComponent.ws