It is a fascinating subject and exciting project. It is true some hill forts have been extensively excavated, for example Danebury, with so much learnt from those excavations. The small museum in Andover which is more or less dedicated to Danebury is one of the most interesting I've visited.

Also there are lowland camps, though few remain, which could throw up yet more information about the Iron Age. Some still exist on nature reserves, in local terms (I live in Wiltshire) I believe there is one on Blakehill Nature Reserve near Cricklade, not too far from the source of the Thames. There is also Ringsbury Camp nearby which to all intents and purposes is a hill fort but a fairly low level one.