I think that would do splendid, after all, the best Roman is a dead Roman, and you will ensure you lots of Britons to smash those pesky invaders!
There can be no doubt that the success of the attack on and stand against the enemy at St. Lambert sur Dives can largely be attributed to this officer’s coolness ... London Gazette, no.36812, 27 November 1944
Welcome aboard! Those add ons sound like a really good idea, they will add more bulk to your armies and variety. The veterans set is my favourite roman box.
Like you I have built both sides, British Celts and Romans and my Britons (when all painted) will out number my Romans by about a 2/3 ratio, with 3 Britons for every 2 Romans, but some of my Romans are Auxillaries (Warlord do a set but they are currently out of the webstore for a little while, being repackaged I think) who are less value than the standard legionary. To be honest my armies were it for WAB rules not Hail Ceasar, but I would think that if you are talking legionaries vs celts a 2:1 ratio is fine.
You might also want to think at sime point about buying some command figures for each side to represent the generals. I did my Celtic chief in a chariot.
Rufus T. Firefly: Oh, I'm sick of messages from the front. Don't we ever get a message from the side?