Wallands CP school in Lewes has a nursery class attached that takes kids from 3 (funded). DD went there until we moved to Oz and would have moved up to the primary school with her brother. I was happy with it - it's a good school, bigger than some in Lewes, but to me that meant better facilities, more friends etc.
Southover and Western Road primaries have good reputations, but don't have pre-schools. Southover is C of E and is particularly sought after. Tbh the majority of primaries in Lewes are pretty good.
Lewes New School (alternative, independent, part of Human Scale Education) is a gorgeous little school if it fits your educational philosophy and has a pre-school. My boys went there for a couple of years (DS1 Y5/6, DS2 R/1) but I moved DS2 to Wallands in the end as he wasn't getting very far educationally. Turns out he's profoundly dyslexic which they totally missed. The very small classes can be difficult socially as well, and the majority of the mums in the playground won't talk to you if you've had your kids vaccinated though overall, strangely enough, I have a lot of affection for the place.
Get in touch with E. Sussex CC and they will be able to give you all the info you need. Like other places around where you live will determine your choice of school to a certain extent if you're looking at "usual points of entry".
Your other option around that area is the little village schools that are often under subscribed. Hamsey CP is a lovely little school just outside Lewes, Barcombe CP ditto. If they have spaces you don't have to be on the doorstep.