Sorry I'm late to answering the questions, but better late than never right?
1. It depends, but I liked the Squid Sisters's music better than Off the Hook's
2. Hightide Era, their music brings in a sense of nostalgia to me for some reason
3. Octoling
4. I have seven so far: Octoling OCs named Coral, Kelp, Shark (an adult Octoling), and Dolphin (also an adult Octoling), and tentacle Octarian OCs named Clam (Octotrooper), Ocean (Octobomber), and General Anemone (Octohurler, he's the older brother of Kelp and Ocean's mother as well as the brother-in-law of their father).
Character connections: Coral and Clam are brothers, Kelp and Ocean are sisters, Shark (he's extremely skilled with chargers) is married to Dolphin (she's pregnant by the way), General Anemone is Kelp and Ocean's uncle. Coral and Kelp are dating, Clam and Ocean are dating.
5. So one of my headcannons is that female Inklings and female Octolings do get pregnant, but they lay their eggs only a few days before the child is born. A theory of mine, which is mostly confirmed at this point, is that cut-off Octoling tentacles become tentacle Octarians naturally after enough time has passed.