I have learnt a few things in my short 12 weeks.
Bonds fit the next size down better (ie. 000 will fit well were 0000 of other brands fit) I know they stretch a little but it's hard to get baby in. So my advice would be buy 000 bonds wondersuits. I had quite a few hand me downs and I needed them as we had a few poop and puke accidents in those first few weeks. Probably have a good 16-18 suits.
My baby was 8lb and fit them well from day one. She fit 0000 everything else from day one. But I couldn't get her in the 0000 bonds suit very comfortably. Try to think of the seaons your baby will be in around the rough age marks. Sounds like you'd be heading into winter so i'd stick with the wondersuits as they are so easy. Things like that that buttons up the front are good. Although I have found those really cute fluffy type full body suits ( seen at target and Big W) tend not to fit so well around the legs and if they are a tad too big the legs come up out and the baby gets all tangled, they're fine when they fit just right.
Full body outfits that button only at the bottom have to be slipped over babys head and are difficult to get on. This os not so much the case with the ones with no arms or legs. They are easy to get on.
Two piece outfits, although cute, are a pain in the but for a little baby that you have to handle alot as the top always works it's way up. Leave them till sitting/crawling type age I'd say.