I'd suggest ~10 short-sleeved vests, 7 sleepsuits, a couple of nice warm cardigans with and without hoods, a nice warm hat, and a couple of blankets.
Also, indulge yourself and get 2 or 3 of the cutest outfits for LO to meet the grandparents etc.
We wished we'd bought more in newborn sizes than 0-3. Unless you have a big baby (9-10 lb) 0-3 will be huge!
We used a cellular blankets to swaddle DD for the first few weeks until she hit 8lb and was big enough for a sleeping bag. I do recommend getting a sleeping bag, we really haven't looked back and I have friends who used them with a moses basket. Continually reswaddling after night feeds and when baby wriggles out is a pain. We had a couple of those shaped swaddling blankets that we really didn't get on with (2 big for our little DD).
I agree about the snowsuits. Too warm if baby is asleep and you stop for coffee. We put DD in a big cuddly (Grandma-knitted) cardi and put a blanket over which could be taken off indoors without waking her.
I don't know if you have your buggy yet, but I'd strongly recommend one with a carrycot. The HV bang on about babies spending too long in a car seat and if you're anything like me the guilt will get the better of you if they do a long sleep. DD slept beautifully in the carrycot - as well as she might in her bed - whereas she'll only do 30 min in the buggy now.
Another thing... LOTS of muslins. 20 isn't too many.
And a DVD box-set - I used to watch an episode of House during night feeds in the early days and while she slept in my arms in the day. It has to beat daytime TV!
Good luck!