Mine were both under 5lb. Size 0 nappies, definitely.
DD1 was smaller and we had some stuff from Next for her that was their 5lb size. That barely fitted DD2, who was longer, so she was in more the under 7lb size. So you might want to have a few bits in both sizes as it'll depend on the proportions of your baby really.
If you want a sling, a stretchy wrap one will be more likely to have a low weight limit. I've had a Close Caboo, lower weight limit 5lb, and also a BabyBjorn structured one which is great when they're older but the lower weight limit is 8lb. DD1 couldn't have used that till she was about 4 months!
You might want to check whether your car seat needs inserts, ours didn't but I know some do for very little ones.
Also, the midwives will probably tell you this, but co-sleeping is advised against for babies born under 6lb, so you might want to make sure you've got a good sleeping arrangement set up with baby on a separate sleep surface. A lot of sleeping bags also have a lower weight limit. We used blankets, very carefully tucked in, till ours met the weight limits, but I'm sure you can get small sleeping bags.
On the plus side, tiny babies are much easier on the arms and back!