What's a good handicap for a less experienced player in an MTG Draft?
To be contrarian: in my experience, if you're adding a sufficient number of new people (which it sounds like is the case here), I'd encourage not handicapping them at all.  My recommendation would actually be to start not with drafting but with some form of sealed-deck play (maybe a simple three-round league or the like), so that the new players have fewer decisions to make and can learn what the core elements of a limited deck are.  Once they understand the essentials of limited then just let them loose on a draft - the experienced players may well run the table, but the newer players should still be able to have interesting games with the experienced drafters and excellent games among each other (this is why you need a sufficient number of new people), and IMHO the (slightly) 'deep-end' approach (along with some measure of coaching, post-draft analysis, etc) is the best way to get truly interested players motivated to get better.

One plausible alternative, though, that might be worth looking at is some form of team draft/sealed, where each of the new players is paired with a more experienced player that they can directly watch, talk with, and learn from; 2HG is a tough format to draft (as opposed to playing sealed with), but it's a great and underutilized choice for this sort of thing.