Love it! I'm collecting Celtos again myself, as they were the line that dragged me back into wargaming after a couple decades away.
I'm deciding on rules. Of Gods and Mortals has a pure Celtic supplement, complete with chariot rules. Before the Gates of Troy has all the things needed too, despite the obvious setting difference.
It may end up a homemade bash of the best of those games with a little Lion Rampant, and maybe some Test of Honour?
Regardless, keep at it!