Hm.. well step by step what I did was...

Install sts

Subscribe to the mods I wanted (specifically, mod the spire, downfall, and minty spire, plus the mods those require)

Launch the game with mods

There's a black screen but it kind of flickers into view when you mouse around.

I clicked the check boxes next to the mods, then clicked play

I suppose some mods may not work. It could also be the mod load order matters and that is throwing errors. Although I did not research into that and whatever order it was in by default is what I used.

Works ok for me, but I'm trying to figure out if there's a launch command to go right to the game, so I don't have to deal with the flickery launcher each time