How many guild coins do we need to unlock the raid?
it depends on the tier. Tier 1 is 30K going up by 4K per tier until tier 6 which is 55K. Price of Tier 7 isn't known since you have to beat tier 6 to unlock it first, and no one has played the raid yet.
Most guild seem to be aiming at doing Tier 5 to start (5*+ characters recommended for level 70+). tier 6 is 6*+ and recommended for level 80+.
There's no raid strategy really. The developers released packs of characters (don't buy these) with recommended heroes you can look at. I imagine those are the heroes they used to beat some challenges.
The only thing I'm fairly confident in saying is that Taunt will play a rather large role, so you'll want a Chewie, ST Han, Poe, RG (or all 4) at a high star level. A Healer almost goes without saying. Debuff removal seems like a very large plus but (IIRC) you can only get that with Ackbar, Ewok Elder, Lobot, and Barriss (on a pure jedi team, and there's no jedi taunter...).