Tuesday and Thursday* 5-8PM PDT for progression (Food, flasks, fully enchanted and gemmed, expect lots of deaths). I wouldn't say "hardcore" expectations, but we started this raid team up for members who want to put the extra effort into raiding this expansion. Still all about having fun!
Friday is like an alt/gearing Normal run. Probably where you want to start if you can make it once you hit 110, but it's not mandatory for the progression team or anything.
You do want to talk to Zoologic/Biggie, but I'd say hit 110 and plan for Fridays first. If all goes well we will be clearing 10/10 Heroic soonish and might start into Mythic if we have enough consistent people, and probably wont be able to carry/gear on Tues/Thurs. Meaning there will be DPS/gear requirements for those nights.
But like I said you got to talk to Zoo about that, I'm not the authority and will likely be taking a break from WoW soon (been raiding since Legion started, need a break
). Get a guild invite from anyone in "The Guardians FM" and send him an in-game mail if he's not on (not sure how often he checks PMs here on the forums).
Edit: I'm not sure if there is any specific role, but I want to say a tank. Having extra tanks is better than not having them
. You can play what you want though. If you're having trouble picking a class you can give us a short list of the few that interest you.