Caching Model Format: shadow caching questions

We will silently create optimized versions of all used 3d models.
Those "shadow" copies must be stored somewhere.
Some questions arise:

1. Location of this storage.
2. Size of this storage.
3. Lifetime of shadow copies in storage.
4. Do we need to provide API to maintain this storage ?
4.1. Option to turn this shadow caching off completely (can be useful for 3D artists) ?
4.2. Option to turn off caching for some specific model ?