Okay I probably should have just edited my last post.
c. If Arbok were to get Vampire, I think it should be limited to just contact moves. (Poison Jab, Sucker Punch, Aqua Tail: yes; EQ, Seed Bomb, Gunk Shot: no.) Considering that regular Arbok starts off with an Intimidate drop, then that it can start using Stockpile (or Coil) while the opponent switches out, it might become too easy for Arbok to become nigh-indestructable if all its moves gave it recovery.
d. I think equal physical and special attacking stats for Raichu should be considered, at 60/140/55/140/80/130. Mega Charizard X is an example of a pokemon which has equal attacking stats at 130/130, and Mega Lucario is pretty close with 145/140. It would be pretty fragile, although Mega Lucario has shown that that's not always a bad thing.
e. For the most part*, all current mega evolutions only have their BSTs raised by 100. Is it okay to break this rule? If so, Sandslash's new BST looks good. I think the ability might not be very beneficial, though. Ground/Rock typing only if it gets Sandstream (to boost its sp.def), although I don't think it'd need that ability.
*As far as I know, Mega Alakazam is the only mega who has a BST raise of just 90, but this is probably due to the fact that regular Alakazam's stats were raised by 10.