Welcome John, already good advice has been offered. What I will stress is take your time, the looking, trying out, wandering around, long debates over alcohol of should we/shouldn't we, oooooo, its got one of those! This is one of the best bits of boat ownership and it is to be enjoyed. The main initial thinking is around a basic lists of "must haves"! Its also well worth while looking at boats away from the Broads area as they do carry a price premium similar to the Thames.
Most of all, enjoy it.