If ye are really that interested in lPRIA Britain, there are a couple of books you need to have a look at.

Iron Age Communities in Britain and Ireland, Barry Cunliffe. The bible.
An Imperial Possession, Mattingly. Excellent.
The Britons, Snyder. Very Good.
The Iron Age in Northern Britain, Harding
Prehistoric Britain, Darvill
Ancient Britain, Dyer
The Forts of Celtic Britain, Osprey

I have to say that the suggestion that 3rd BCE Britain is not prima facie worthy of at least one faction is totally ludicrous. Do some reading.

Even as early as 272 BCE, Graeco-Roman influence was becoming profound in Continental Celtic/Gallic societies. In Britain we have the chance to imagine a society with much less cultural adulteration. Also, the archaeological record is tremendously rich. Cissbury, Maiden Castle and Danebury are some of the largest multivalate hill forts in Europe. Hengtisbury Head was one of the busiest ports. Some of the best overall examples of Celtic craftwork, shields, helmets, swords and chariots come from Britain.

The problem of course, is that the historical record does not begin until much later, so that we do not have a narrative to rely on for our story: but does that mean that we should abandon these people to the dustbin of history? In EB we are more inclined to take up the challenge and attempt to speak for history's silent people. All it takes is a little creativity.

Re: the name. I won't tell you what we are going to do about that yet. 'Casse' is of course a guess, as we don't even have numismatic evidence for the period, but it is a very good guess nonetheless. The Cassi are one of the tribes mentioned by Caesar, who is basically our earliest textual source, and in addition 'Cassi' is an element in many other kinds of names. But there are some other possibilities. Anyone know what they might be?