Nice. Let me give you some unasked-for info:
- Shinsengumi: supposedly they were not wearing any uniform at this time, although they had used to (the famous white and blue ones), although in "Sword of the samurai" they are depicted wearing a curious uniform black and red colour, so your choice (BTW, don't think on western-style uniforms: they wore traditional samurai attire). Another shadowy question is if they wore armour or not, but they were wearing chainmail armour during the street actions in Edo a few years before the war, so I guess it's your choice.
- Samurai and ashigaru: well, at this time the daimyo's armies seemed to have completely lacked any kind of uniformity. The ashigaru of the XIXth century were the lowest-class samurai, not the peasant turned soldier od the XVIth century. They wore a horrible mix of armours, from archaic-style (kamakura period) to the bullet-proof nambanjin armour of the late stages of the clan wars. Anyway, it seems that most of them had discarded the leg protections (suneate).
BTW, are you thinking about providing them with cavalry? And do you know museum miniatures' samurai range?