What sizes do I need to buy?

I am 36 weeks pregnant and finishing up the new baby's wardrobe. I want to be prepared for more than just month down the road. First, what kind of clothes should I buy for the weather? I'm due April 20th. I have plenty of sleepers and onesies in sizes NB and 0-3. I have 3 pairs of NB cotton pants, 4 pairs of 0-3 pants, 2 Pairs of 3-6 pants, 1pair of 3-6 overalls, and 1 pair of 3-6 shorts. I have clothes bigger than that, but I have them put away and I'm not going to bother with until the time is right. I guess my questions are what size should I start getting summer clothes, how many onesies/t-shirts are going to be appropriate for size 3-6, should I get more cotton pants in the smaller sizes (nb and 0-3) or do you think pants are going to be too hot? The pants that I have aren't thick but I just worry. Also is there anything else besides socks, mitts, hats, and shoes that I'm missing in the wardrobe that's handy to have?