Hi, the memory requirements are high just because once you allow maximum of the chests to be 100x100 the game needs to create prototypes for all chests which are smaller or equal, in each dimention. The memory requirement increases by factor of 4th power based on chest dimention. That's why there is so much mod setting regarding maximum chest size and even whitelist of dimentions.
Inventory size is not that problematic, because all those inventory spaces would still have to be prepared in game if those chests wouldn't be merged. And UPS impact of the mod is same as any other entity played in the world, very small.