I play a Sith Sorcerer in nearly full rakata in a casual guild. Still working on EC, but we mostly run EC/KP HM to have some fun.
1) No, Armourings do not hold the the Set-Bonus in SWTOR until you get to the latest Tier. They are on the armour "shell" and not movable. So switch away with the mission support armourings on your BM Gear.
2) Black Hole gear can be obtained by doing the weekly quest on Corellia (easy), the weekly Rakghoul FP quest (hard) and doing Ops, notable EV or KP Nightmare or the new one Explosive Conflict.
3) Crit crafted orange gear is superior because it gets an Augment and this means a plus to your main stat. Putting Rakata mods into a orange with an augment gets you something like +18 of you main stat, compared to the Rakata original.
Drawback is that you loose the set bonus.
Campaign gear has its bonus on the armouring, which makes crit orange gear + augment + campaign mods the "Best In Slot" item.
4) I think the fastest way to get PVE gear as a tank is to get on a guild run EV HM as off-tank. Not much in the way of mechanics there, and you can get a lot of Rakata if your lucky.