What's written here is vera vera good, but it's lacking in ranked tips, leaving it feeling a bit too general. Was checking to see if we had a hydra guide before thinking further into writing one m'self, and I guess I could do one for both/just vanilla hydra, but you have the custom fairly well covered.
ONE tidbit I want to yammer on about is a few of ability suggestions.(so feel free to throw this out the window if you so choose xD).
First, swim speed. I run it specifically for the reason you stated, to beat the nerfs, but I think you are down playing how good that really is. Squiding is omni-important(ez dat important brotha' =p) when I need to swim away from aggressive squids I don't think I can take on, when I am the only one in position to grab and advance the rainmaker, and even silly times where I try to out-maneuver an in-my-face tentatek(50% success rate, I actually don't recommend it unless you are crazy/bored). The nerf was basically a drop kick to the groin for my play style, the weight of this friggin' gun is acting as a literal ball and chain, and has deepened the chasm that is my hatred of mahi mahi. WHY DO SQUID DIE IN WATER NINTENDO?!? WHY?!??? HNNNNNNNNNNNNNN-
Second, and less fact/more opinionated would be I rarely use charge up( I like the sunny day shirt tho...) The amount of turf this behemoth covers is already quite adequate for getting the bubbler up the few times I tend to use bubbler in a match, combine that with the power of president sprinkler and I can get bubbler up in... less than 30 seconds? I haven't timed it, but it feels really fast. I get by without it, but thats purely my opinion/preference.
Speaking of opinion, numba three. Ink-efficiency/recovery.
I never touch the stuff(well, maybe sub saver once a blue moon).
My reasoning is it already covers crazy amounts of turf with three full charges(thus no main saver), if I don't kill my attackers with 1 and 1/2 charge I'm probably already dead(thus no ink recovery), and I like to stay out of scenarios where I have to clutch throw a sprinkler(almost never sub saver). THAT BEING SAID, I definately tried out all of these in many matches back before the custom came out, and I like to think they helped me learn the nuances of hydra's ink consumtion. Also, your point about getting a full charge after a clutch sprinkler is VERY true.
TLDR for the gear:
I like to make due with hydra's un-altered ink consumption and bubbler charge, and try my hardest to be sanic, ie: all the swim/run speed and ink resistance. Dodge moar bullet, kill with less bullet.
Hope you come back to write in ranked stuff! ~Green Waffles