Mephy is ok, but I hesitate to take special characters in 2k or less, just because they're a huge point sink. He can be useful, though, if you know how to use him.
For the RAS: It's much better to have special weapons (flamers, meltas) than to have cc weapons (axes, fists, swords). Plus a melta gun is always better than melta bombs (that chappie). I would drop a devestator or two plus the melta bombs to get a couple meltas in those assault squads, or if you go slightly over and that's fine just grab them arbitrarily. Or if you don't want to you could even just drop two axes for meltas in one squad flamers in the other.
I would hesitate to have both a raven and a raider at 2k without much else armor saturation (only a dread and a pod) simply because they will not survive long (the raven maybe because it's a flier but not the raider). I would suggest either dropping it and throwing those DC in the raven (mephy can fly so it's all good) or dropping the pod and guard for some extra armor, maybe a baal or two. Just something to think about.
Curious: Why 7 devestators? I would normally run them as a 5 man squad with 2 or 3 weapons. Just makes the points a bit odd.
Hope this has helped a bit!
If you go down to the woods today, be wary