they're both around 30-32k. there's really no significant difference aside from clicks/h (less for cavefish) and that the LRC monsters *can* hurt you. once you get to 86, definitely switch to rocktails with admiral pies. at 86 i was getting 43k xp/h pie-ing.
antipoison - they rarely even poison you anyway. melee: helm - full slayer helm cape - fire amulet - fury weapon - chaotic rapier (whip) shield - dragon defender body - bandos legs - bandos gloves - barrows boots - dragon ring - berserker [(i) if you've got it] with bunyip you shouldn't need any food. if you do, they drop lobsters. when they burrow, step two spaces away in any direction from where you were standing when they burrowed. use piety and super (extreme) pots. cannon helps a ton and reduces the chances of them burrowing (since you can kill them faster so they have less chance to burrow before they die).
it allows for claws + korasi spec, which is okay for rushing in pvp. will be even better when olde-style pvp comes out and you can use untradeables in the wilderness at no risk.
yes. they are low defence and cannonable. you will get a lot of melee, ranged, and slayer xp fast. they also are one of the best droppers of effigies in the game, and are excellent crimson charm droppers.
bones may potentially rise when the wilderness is reintroduced (no more free reign of the green dragons by campers/botters), unless jagex decides to add green dragon spawns outside of the wilderness.
there are people returning with phats, yes. but there will also be many more players returning without phats who demand them. there is not enough information do conclude which cause, increased supply or increased demand, will dominate.