I have rope fish. They like places to hang out, so if you go bare bottom I'd add more than just a tube for them - driftwood, fake plants, etc to keep them most happy. I do have a fully planted tank which they seem to love but I don't think live plants are fully necessary as long as you have décor. I don't think substrate matters as much as what is in the water column. If you just have a bare tank with tubes you probably won't see them much.
Yes, they like to be in groups of 3+. Mine cuddle constantly and it supposedly keeps them more comfortable so they are more active (which mine are). They also hang out in funny places all the time, partially propped on random plants or décor.
Secure the tank as mentioned above for sure, as in duct tape or otherwise over every little hole even where your heater cord goes in.
I love mine to death, (they even eat out of my hand) but if you want a minimalistic tank they might not be for you. I'm not sure they'd be super stressed as long as they had a tube, but I don't think they'd be happy. Ropes are wild caught and come from vegetated areas with plants and reeds.