If you are only going to make 1-2 it is ez enough to do in clean up
If you are asking about production proto type on original model.
There is my 2 cents.
You are 2-3 stages from where you want to get. Your model will get
cast or molded then mold will get injected with wax and cast again.
Each step here will shrink in size from your original.
The shrinkage of 8-10% for molding sounds a bit much. For a
vulcanized (heat & preasure) molds using silicone rubber should be
about 4-5%. RTV (cold molds) are about 1-2%.
Then after casting there will be clean up which will add shrinkage.
Here is what I am doing now for anything that will get molded.
Print out 3 models all scaled in increasing sizes from 1.0125% to
1.05% and pick one that will give best result. Then cast and clean
up. Then mold.
Hope this helps. If you need more help PM me.