I've only grown Elephant Ears for 2 seasons and Caladiums for 1. When my Caladium bulbs were 2-4 per starter-pot it resulted in most with root tangles that I couldn't separate w/o ripping apart parts of the root masses. And this was only with a spike or 2 and maybe a half-grown leaf. They all lived. I grew a 'Frog-in-a-blender' Caladium next to a Colocasia esculenta 'Mojito' outdoors in the ground without any problems. They weren't as close as the bulb root tangles I had in pots though. I've grown smaller Caladiums 6" from Alocasia trunk bases and the only issues were that some Caladiums got a lot of shade. They still looked nice. Colocasia esculenta 'Black Magic' or Colocasia esculenta 'Illustris' have more aggressive root systems. I didn't plant other EE's or Caladiums as close to them. Maybe a foot away. Next year all my in-ground Caladiums will be about 18" apart from each other and larger ones 24" apart. Hope that helps.

I can see the problem with root masses getting entangled. I was sort of hoping to avoid that problem by growing things that can be left in place for the most part. Or things that go dormant so that there is a clear time you can mess with them a bit more. I would love for the container to crowd up nicely with things of different sizes.

I have never grown Colocasias or Caladiums actually. It might be a thought. Apparently C. esculenta is hardy in my zone and could fill up the whole container. I sort of went off those types after I had such poor luck with Alocasia macrorrhiza. And Im pretty smitten by the foliage of Sauromatums and Amorphs.