Centerlock rotors are a Shimano thing... I'm not aware of any non-Shimano Centerlock compatible rotors. You can get them in every price point from a cheap $10 rotor up to XTR. Depending on the price point, you can get either resin pad only or metallic pad only rotors, so in that sense there's no enormous brand compatibility between the rotor and the caliper, although if you're playing it by the book "only Shimano works with Shimano". But do be sure to match the rotor's pad compatibility with the pads you want to use.
The Centerlock lockring for your traditional quick release axle hubs uses the same tool as the Shimano/SRAM cassette lockring. If your hub has a thru-axle it will use the same tool as a Shimano external bearing bottom bracket. The Centerlock lockring itself is different from the cassette lockring though, so don't expect to swap those around, and for thru-axle it's totally different too. Rotors are more straightforward though--Centerlock fits Centerlock.
If you get a hub that uses Centerlock rotors and want to use a 6 hole rotor, you can get adapters for about $20 that work alright although I am naturally always a little suspicious of things like that. I know someone using an adapter who thinks it is the cause of an otherwise un-diagnosable squeal. I've never personally used an adapter.
6 hole is definitely going to have many more options to pick from, hub and rotor wise. For many riders I don't think there's an enormous discernible difference. I make considerations between the two based on desired parts and ease of maintenance. As a mechanic I like things that are easy to work with, so Centerlock is appealing for that. 6 hole rotors have to be tightened in a star pattern (like lug nuts on a car wheel) and often times use a torx wrench so that's slightly annoying but at the end of the day it's no big deal.
As a mechanic I like Centerlock by merit of its design and principle. I own both (ridden the Centerlock bike a lot more) with no problems from either. But I am a little biased towards Centerlock. I have a slight superstition that the rotors are better at staying true but that isn't really backed by evidence... yet :)