i have no earthly idea how vic 3 calculates what land is taken over by rebels

Yeah, unless you have a lot of construction sectors and a high-tech training rate, I suspect you're not likely to train enough troops before they make significant inroads. That being said, America's mass conscription can be a bit of wildcard sometimes.

I normally only face these revolutions if I wasn't paying enough attention, and so justify my save scumming to avoid it. But if you're going to fight them, you're probably doing the best tactics available. Conscript everyone immediately, ensure your big armies have the extra supplies/support mobilizations, maybe consider a small backdoor naval invasion to put them on more fronts (especially if their capital is on the coast).

Ideally, be economically prepared to fight for a couple years at least. Don't worry if a lot of your soldiers die en masse - that just means you don't have to pay their wages. If you're near a new training rate tech, prioritise that. Bankruptcy is not necessarily loss, a 50% penalty (and penalty to training) is overcomeable if you have >3x their troop numbers by then. You can keep an eye on the bourgeois' debt by looking at the "take their debt" diplo option, if they're nearing bankruptcy, then just play it cool until they do, and push for the win.

As for Marxy boy, just bring the farmers into your government, then promote him to be leader of the party. His personal values should sway those of the party and the commie coalition might be back.

Whatever you do, save scumming or not, a glorious salute to crushing their spirits on the battlefield or in making the new socialist utopia