Yes, many here have them and shoot them very well. Call and talk to them. If you have an action, they have a number of options for you. The first one costs a bit more since you have to buy the tools, but after that it's as simple as buying a replacement barrel and spinning it on.
Yes, same here and I'm a bonehead. No different than replacing a barrel on a Savage except use the action hole and cut off hex head bolt to line up the recoil lug with the Wheeler tool. Or you can get the recoil pinned by a smith but I don't like that personally. I use the Wheeler tool and a regular bench vice for the whole job. Sort of combination between these two jobs. I think everybody has a different way of doing it depending on how far you want to go on tools. Honestly, if this first guy can install a barrel nut anybody can.
I run them, spin off the factory barrel, spin on the new one until it touches a go gauge, tighten the barrel nut and youre off to the races. Northland will sell you everything you need to do this and they are at a very reasonable price I feel.
I stayed 223 on one and the other 6xc was a new action so nothing there to replace on that one.
If youre wanting to switch it up a 223 has a .384" bolt face. Means you can go 223ai, 204, 222, 6x45, 300bo, 20 prac and a few more but those are the main ones. Some have factory ammo options, some dont.
If you wanted something else thats larger you would need to have the bolt face opened up or you need to get another bolt for it, ptg or something like that. I would get a new one piece bolt before I opened it up. Those arent home smith jobs though like a remage is though.