As far as maximum print dimensions from 35 mm go, the answer is "it depends". Some of the first rock/ice climbing and mountaineering images I sold in the early 70's were shot on 35 mm Tri-X, often pushed for contrast and grittiness. They became poster-sized adverts for an equipment manufacturer and were mostly printed at about 3 ft x 4 ft. The sharp grittiness suited the subjects.
Earlier than that, when I was still using the cheapest enlarger and lens there was (a Gnome Cadet), I was very disappointed with big enlargements from 35 mm - but that was a problem with the lens. That is a key issue with big enlargements - use good lenses, if necessary those made for high enlargement factors, like the Componon-HM or Apo-Componon-HM. These are relatively cheap on
eBay. I find that it isn't the film's graininess that is the issue, but the way in which the graininess is rendered. I have plenty of 2 ft x 3 ft enlargements from Kodachrome 64 slides and they look very detailed, without any distracting graininess.
A similar issue exists with digitally printed images - I strongly believe that you need to scan at more than 4000 spi (real spi, not manufacturer's marketing fantasy spi) to get the best enlargements. 8000 spi is good - you are trying to get graininess that is a true representation of the film, not grain aliasing or imitation. 8000 spi will get you an excellent 20x to 30x enlargement, maybe even 40x.
It helps to start out with a high quality image - any problems like defocus or shake that are imperceptible at low magnification can become obvious at high magnification. This is also partly affected by the common practice of printing larger images with a little more contrast than smaller images.
Best,
Helen