1) Yes, it used to be hard as fuck to get. Collect two more and keep a shrimp and a squid and an amberjack to make its future ult form, which has 4 heal awakenings, a light row, and two poison resist. And really nice stats.
2) Squid drop way more, but you still have to evolve them. I'd farm the mugs myself.
3) In every case I know of, yes. Why? I have no idea.
Anyway, finished Star Vault using the skillmax ROdin I BF'd today. 58 +eggs for 5 stones, not too bad. Would have been 4 if I hadn't majorly botched my rank up (ended up having 2 stamina left and 1000 exp to go and waiting would have been a waste of time orz).
It'll be even faster and better once I skillmax my own ROdins so I can farm it even faster.