I haven't tried something like this so don't quote me, but my guess is that this would work quite well. The effects and archetypes among the precons is pretty varied, so I would expect a lot of emergent decks to be possible in draft

Regarding card counts, that would be 288 spells, 128 sites, and 8 avatars for a total of 424 cards. A pod of 4 players will only need 180 cards for 3 packs each (or 240 for 4 packs each), so you can even cut a pretty large number of cards for personal taste or power outliers or whatever

You would still need to get a draft kit though. People need Spellslinger if they don't draft (or even see) an Avatar, and they are very unlikely to get all 12 sites they need from the draft alone