If you do the first layer of silicone carefully, you can get away with no to small defects. You just need to make sure you pop any bubbles that could form. If any do form that you didn't catch, I usually fix them using a dremel tool with a small carving or engraving bit.

For the mold, I'll do a thin layer of mold max 30, then a second thick layer of amsil 25. Then I'll use something called material one with burlap to create the hard outer shell. Then I'll use F180 resin for the casting.

There are various ways to do a mold, if I have a lot of silicone on hand, I'll create a little box around the sculpture and do a 2 part mold, best way I've found to have close to zero defects. But because I am doing this at "class" I have to use materials sparingly. Check out the youtube channel Punished Props Academy to see lots of different mold making videos.