Yes you can have any scale you want. If you got X 256 Y something Z something then it would snap modularity on X but not on Y Z. For some meshes this is fine. It all depends on what you are doing. Combination = 32+64=96. It doesn't has to be 64 128 256 etc only. 108 for example is fine also. As it is 64+32+8+4 which is…
The grid in Unreal is a power of two, so your meshes must be for example 128 units long to easily snap in that grid. Since you work with a grid of 1 in Max you'd need to set the grid to 1 in Unreal also, which would greatly slow down your work flow. Also there is a possibility you got export scaling enabled or some other…
Can be any size you want but if you want it to snap to each other easily it needs to be 32 64 128 256 512 etc yes, or any combination such as 192. For non modular it obviously doesn't matter, like a tree.