1) I was going to use 3 coats of rebound 25 I only have 2 of the trial size so 4lbs is this enough and how much would you use per layer?
You might be able to get the whole thing covered with one trial set, if you're stingy with the first couple of coats. When I first started out doing molds, I found that one trial set would produce a good mold for a single mask. But they were only half masks, not the whole thing like you have, so YMMV. For a good production mold, you probably want at least 4 coats of Rebound 25. For the first "paint coat", you may want to use a little of their thinner in it, if you have some. Not entirely necessary, but it will help flow into the nooks and crannies really well, and also help reduce bubbles. They say Rebound doesn't need to be degassed, but I still get bubbles in mine if I don't. Even unthinned, Rebound spreads out really thin, so you don't need to mix up that much. Maybe 1 or 2 oz. of A and B. Better to use less at first, as you can always add more. Too much, and you're always scooping it up, and pouring it back on top, to avoid wasting.
For the second layer, I usually go unthinned. But still using about the same amount.
If things are not looking like they have a good coat on them, you might want to do one more coat, with just a few drops of thi-vex, just to get a slightly thicker skin on there, before you start spreading around the really thick stuff.
Third coat, you want to thicken quite a bit, kinda like peanut butter consistency. Start with about 15 - 20 drops of the thi-vex, and see how it feels--you can always add more, just don't go overboard. Use this to fill in all the deeper holes, and undercuts.
Depending on how well that went, you may need to do another coat like that, or just one more which is a bit less thick, to help even out the surface.
One other tip (you may have seen), it is really helpful to pick up any color of the silc-pig silicone pigments. With that, you can tint every other layer, and really tell how well you are covering things. Otherwise, it all looks pink, and you can't really tell what you've done from layer to layer.
2) I have trial size of plasti past as well I hope this is enough should I just mix up the whole thing
I haven't used a trial size of the plasti-paste, but you might be able to cover the whole thing with it. You probably don't want to mix it all up at once though, because this is going to require a 2-part shell, otherwise you won't be able to get the castings out later. Depending on how you go about that, it's possible to do it all in one go, but usually people do it one half at a time. There's also a method I see guys like Volpin use, where they join two pieces of plywood, cut in the profile of the mold, and then use that as the center joint, and run all the plastipaste at once, on either side.
3) is mold release 200 good enough to use on the sculpt or should I also use smooth on wax to help release the mold from sculpt as well how many coats of mold release 200 do you guys use?
With Rebound, ease release 200 will be more than fine. I would NOT wax it-- the rubber will pick up that detail (it can even reflect fingerprints), and ruin your end result. Spray it lightly once, and brush into all the cracks. Let it sit a few minutes, and then hit it again with a light coat. Shouldn't need more than that. Let it sit for 15 - 30 minutes before you start putting on the rebound though. I do put the sonite wax on top of the cured silicone, before I apply the plastipaste though. Not entirely necessary, but it helps lube things up a bit, and make it easier to remove later. It's also necessary to use between shell halves, so the plastipaste doesn't stick to itself (also helpful to put aluminum foil in between).
Sorry, lots of typing, hope it makes a little sense at least.