If I have 3 artifacts and 1 Inventor's Apprentice. Does my apprentice get +1/+1 or +3/+3?
Inventor's Apprentice gets +1/+1 as long as you control an artifact. It's only +1/+1, and this is true no matter how many artifacts you control. If it was the other way, it would say "Inventor's Apprentice gets +1/+1 for each artifact you control", as it does for Cranial Plating.