My friends and I all chipped in to buy a booster box. We plan to draft with four players. FFG recommends 6 players with 6 boosters each. Since everyone chipped in, we want to deplete the whole box. Would 9 boosters per player work? If so, should we do something like 1st round 5 packs, 2nd round 4 packs or do 3 rounds of 3 packs each?

Side question: How is everyone distributing legendaries? Keep what you draft or do they go back to the pool at the end of the draft and winners get first choice?

Number of boosters to divide a box up between friends is irrelevant really. 9 each is fine.

What my friends and i do for legendaries is they are part of the rotation like the other cards, but when were done we regather all 6 legendaries and starting with the person that won we pick one. With 4 people i imagine you'd just loop around and 1st place picks the 5th legendary as well as the 1st.

We just keep the nonlegendaries we grabbed via the roundrobbin. None of them are really worth the effort to put back together like the legendaries, if you want any of them thats what trading is for.

Snake draft for sure whenever you are drafting for product. The first 2 people will be getting the best legendaries (Luke/snoke/cassian/mortis/etc.), and that is worth the 9 boosters that they purchased. If they get to get the extra crap legendaries (formidable/stealthy/wheelbike/etc) as well, that leaves 2 people with 9 booster purchases for a 5th brother saber/Hailfire/Planetary Bombardment and nothing else. Snake draft fixes this and the people who get the "medium" legendary because they pick last also get a"crappy" legendary because they pick first on the way back up.
Long story short, when drafting for product, follow this Picking scheme:

1st,2nd,3rd,4th,4th,3rd,2nd,1st,1st,2nd,3rd,4th,4th,...etc. (it's called snake draft)