Would painting a foam plane with acrylics actually hold up, or am I wasting my time?

Hand-painting foam is absolutely a thing, and it holds up better than you'd think. The crack-and-flake fear mostly comes from people slapping thick coats of house paint or spray can stuff on bare foam. What acutally works is this: give the foam a light scuff with fine sandpaper so the paint has somethig to grab, then seal it first. A thin coat of white glue mixed with a little water, or a foam-safe water-based primer, does the job. Then your acrylics go on top and they flex right along with the foam. Foam wings barely flex anyway on a small trainer, so wing bending isn't really your enemy. The bigger enemy is fuel and sun, and on a electric foam plane fuel isn't even an issue.

The finishing move is a clear coat over the top, and that's where people mess up. You want something water-based and flexible, not a solvent spray can clear, because the solvents in some of those will literally eat foam into mush. Test any clear on a scrap piece of the same foam before you commit. Two or three light coats of a water-based poly clear over your paint and it'll shrug off handling, hangar rash, and sun pretty well.

One warning from expirience: paint is heavy. On canvas nobody cares, but on a little foam trainer every gram counts. Keep your coats thin, go easy on the white, because white pigment is the heaviest and everyone wants to paint white on these things. A hand-painted wobbly look actually suits foam great, and honestly a slightly imperfect finish on a first plane is a badge of honor. Also, buy a cheap spare airframe or two if you can. First planes tend to meet the ground in ways that test your paint job. Nothing worse than spending twenty hours on a beautiful red, white and blue scheme and then stuffing it in on flight three. And since you paint airplanes anyway, keep your sketches. Once you've flown a season you'll know exactly how you want the next one to look, and there's always a next one. That's how this hobby gets you.

Painter here too, made the jump from canvas to foam a couple years back. The one thing that changed everything for me was low-tack masking tape. Regular tape kept pulling my base coats right off, but the yellow stuff for delicate surfaces lets me lay down crisp stripes without the heartbreak. My scheme is all hand-cut lines and it still looks sharp after two seasons on the field. Only catch is you have to let each color cure a day or so before taping over it, which tests your patience when you're excited. For the wobbly hand-painted bits I just use cheap synthetic brushes and don't overwork them.

Following this one since I'm in a similar boat, except my painting background is miniatures, so tiny brushes and obsessing over details nobody will ever see. The weight thing never even crossed my mind, I'd absolutely have caked the thing in layers without thinking twice. Does anyone know how well this kind of finish holds up to being handled alot? I'm clumsy and I figure I'll be grabbing the thing constantly while figuring out how to even launch it. Also slightly terrified reading that first planes meet the ground a lot. Maybe I should practice the scheme on paper a few more times first.

That scheme you keep painting sounds a lot like a Decathlon, red white and blue with fat spats is basicly their signature look. There are foam versions sold already finished close to that, so for a first plane I'd grab one ready to fly and save the brushes for airframe two. I put about 60 flights on mine last season before it earned a repaint, and by then I knew exactly which corners take the abuse. Paint your second one bare and go wild on it, because your style will change once you know how you actually fly the thing.