I rmeber having read that at the start of WWI the germans mistook the british firing drill for Machinegun fire.
I think it is not about whether certain weapons are really available, but in what amount and with which tactics.
I can therefore imagine very well MG in VSF, as well as a steam-WWI with tanks etc.
And the colourful Uniforms - it is difficult to assume that from 1850 - 1910 the technology had a break from evolution. One might have to decide about the technological and tactical setting.
In RCW, there were MG (many), cavalry charges and also occasionally colourfull uniforms as well as tanks, AC and trains.
I don't see a problem to let this happen 20 years earlier, really.