No, you don't get to choose characters, because finding out who is who is basically the main part of the game.
I think Enjolvert's suggestion is a really good one. Start with just Mafia and civilians, or in our case National Guard and revolutionnaries and maybe one person with special abilities on each side. I'd suggest to start with the two characters often known as the detective, who can enquire during the night who are the Mafia (so maybe in our case a Gavroche who can enquire who is national guard) and the terrorist (see my earlier post) who can stop him from telling what he found out (maybe in our case we could call that person "the cannon" or the "hail of bullets"
Then, once everybody got the hang of it, we can put more and more persons into the game, maybe even develop them together, because right now it seems as though not too many persons could join the discussion of what special abilites characters get. It's also important to keep the game balanced.
Btw, enjolraslesunicorn, you suggested a Thénardier who robs the dead and finds out about their identities. Why that does make perfect sense in the context of the book, the identities of the dead are usually announced after their death in Mafia anyway, at least that's the way I know it. The character known as the thief in the set of rules I know is able to steal the special ability of another character (usually living, but we could change that for Thénardier of course...), who could then not use this ability for that night (but wouldn't be told) while the thief could use it. The thief may or may not be told what special ability he stole (a Thénardier who'd rob the dead would of course (usually) know what special ability he got his hands on, but that's not so bad, because a thief who doesn't know what ability he stole can really mess up the game).
I'm looking forward so much to actually playing this!