Lakenheath are usually very helpful and you should have no problem with or without a transponder although they are always happier with one. Should be relatively quiet at the weekend. The F 15's stay largely tucked up although the flying club might be operating.
Lowtimer gives some very good info and as he says, watch out for the danger area. This is often active at weekends as is the para dropping although a bit cold at this time of year. Some of the neighbours are a bit sensitive about noise at Old Buck and they prefer you to avoid Attleborough to the north of the field on the A11.
It's a very friendly airfield and you should have an enjoyable visit