Unlocking a sector is pure RNG, your stats don't matter for it. You can use shark parts all the way up to 80 if you wanted to.

The generic best build is C+U+Y+C+, so if you wanted to get a jump start you could craft yourself a CUYC sub then upgrade it to the augmented version at 80.

You can also join the FFXIV Submarine Builders discord server to talk with more people about subs.