V-wheels, linear rails, or bushings for the carriages?

Any of them works because the loads are tiny; pick by budget and precision. V-wheels on extrusion are the cheap, forgiving favourite — easy to build, easy to adjust, plenty accurate for foam. Linear rails (MGN12) are smoother and more precise and look great, but are overkill and pricier. Bushings/LM8 on smooth rod are cheap but can develop slop and need good rod alignment.

Whatever you choose, the killer detail is eliminating rock and play in the carriage: a wheel that wobbles or a loose preload acts exactly like backlash. Adjust eccentric nuts so wheels are snug but roll freely, and check both towers feel identical.