There're several limits related to animations:
1. FNIS limit - the first one which player will meet if installed too much animations. Fore increases the limit each release of XXL version of his priceless tool. As for now XXL version limited to max 26162 animations. On that limit I can't affect, Fore sets it himself in his tool. 
 
2. FootIK limit [LE Only] - when we initailly loading a gamesave with too many animations there's a chance to get FootIK startup error. The error can be skipped with gamesave preloaders like Continue Game No Crash, Load Game CTD Fix or with animation preloader in Animation Loading Fix (be aware, only version 1.0 is compatible with the patch). The problem seems to be fixed in the SSE version.
 
3. Register limit - the game has internal limit of some objects (units) related to animations - 32768. When we pass the limit we get 0xBE6DD3 CTD. This fix was created to avoid exactly that limit.
 
4. SexLab limit - the maximum amount of animations the framework can store in its registry. This limit related only to the framework. ZaZ, DD, TKDodge and other non-sexlab animations has no affection on the limit. Can be expanded with a tweak shared somewhere on LL.
 
5. Memory limit [LE Only] -  animations, as game-objects commit some space in the main memory block (block 1). There're many tests and words was written related to this, the only thing you should know, when the block overflow crash happens (unless you play the SSE version of the mod where the block was largely increased and should never overflow). You can adjust the size of the block with DefaultHeapInitialAllocMB option in SKSE.ini, or you can try to enable UseOSAllocators in CrashFixPlugin.ini, which split the block data in shared memory. I also recommend to use ReduceSystemMemoryUsage in enblocal.ini to free process memory from texture data. 
Note that:
- If you set DefaultHeapInitialAllocMB more than 768 the ExpandSystemMemoryX64 option in enblocal.ini must be disabled.
- If you enable UseOSAllocators the game become much more sensitive to game files correctness, what may bring additional random crashes if something wrong.