That wouldn't significantly affect most galaxies though, would it? The rasin bread model might insinuate that the space in a galaxy isn't expanding (which is wrong), but it is accurate in thst gslaxies themselves are not growing larger.

Yes, all distances are expanding, but not everything in space is expanding. Atoms aren't expanding because atomic forces are far stronger than expansion is, for example.

Yet the distance between galaxies is increasing, so there must be a crossover point where one structure can stay structured but a slightly bigger structure is torn apart.

My question was if this size is larger or smaller than galaxies, and it seems to be quite a bit larger than galaxies at the moment.

The interesting thing is that the expansion is increasing, so this size limit is shrinking. Unless some change in forses happens (like inflation or some kind of false vacuum collapse) the limit will eventually be smaller than galaxies and they'll get ripped apart. Eventually star systems will be ripped apart too, then stars (if any remain at that point) then planets, molecules, atoms, and bosons; and if if that continues to quarks funny things start happening that kind of look like the big bang.

That last part is still speculation of course, but I do still wonder if the expansion of the universe affects galaxy formation and dynamics, and if ancient galaxies were different in part because of this.

Yes, but just because the discrete distance between 3D points isn't constant does not mean a 4D space exists that allows for what is being proposed.