i worry about my indoor bunnies getting too cold and leave heaters on (low) for them overnight, which i wouldn't do for myself.
In our experience rabbits tend to be healthier outdoors. It is more natural for them, than being in an artificial environment.
Not at all, rabbits are built to live outside
Being in hutches/sheds/runs is still an artificial environment, though I do know what you're saying - I think it's snufflebuns that often benefit from the fresh air outside and don't tolerate central heating well isn't it? Equally I'm sure there are conditions where the bun would benefit from being indoors.