I washed everything prior and still had to run out and get newborn items for her since we assumed GD = big baby (we were wrong!).
As for socks, yes, get lots... but we found we lost a lot less if I used a delicate items/zippered laundry bag and pinned it to the hamper to use for socks/mittens/etc. I had two that rotated and they seemed to cut down dramatically on the lost sock issues.