I think the Luna is the easiest Blaster. Because well, you just need to get in range... After this your chances of killing are very high, possibly by exchanging (which is not great of course). But basically, you can find lots of Luna with Respawn and possibly Stealth Jump. This is the easy way, it's kinda efficient, but I wouldn't recommend it for improving purposes.
I hit S+99 with the Custom Range Blaster. I would say it's easier to play solo with this one than the regular one, because of the Kraken which will save you more often than the wall. Plus the Splat helps quite a lot to kill, combined with one shot, which gives flexibility. It's easy to trade with it too, like "oh I'll die hm... Here I'll give you that Splat Bomb". Though the regular is good too, and I would especially recommend it on Saltspray SZ. Personnally I'm not as good with it because I can't use the wall too well with this weapon, and it increases the ink problems. I would basically give it to teammates and swim away to prevent any ink problem on my side, but that's not great in solo, especially if the player is not used to walls (he'll die from a bomb).
About stuff, I'd recommend putting enough ink related bonuses to have 4 shots after playing your sub (instead of 3). At least, if you often die because you lack just one shot, you must do it (like me). For the others, it depends of mods and playstyle obviously, but I think you'll never be bad with some swim speed, possibly some Special related bonuses, and possibly respawn. I feel Cold Blooded isn't necessary for the Range versions, as you have enough range to fight, but that's still possible. I wouldn't play Damage Up as I very rarely have to hit 3 times to kill. Defense Up is questionnable I guess.
About jumping or not, I'd say you have three choices.
1- You need that one shot kill. Then, don't jump, you'll be far more precise (or see 3, possibly).
2- You don't need it. If you're fighting with someone, not jumping is a suicide move. You're increasing the chances to kill, but not as much as you're increasing your chances to die by being too slow. Basically, you'll exchange at best. So, moving (with jumps) is far better.
3- The way you aim when you're jumping and the way you aim on ground are a bit different, and that might be a problem in some cases. If you're not confident in your aim while on ground, then remember you can shoot at the end of your jump. This way, you can be fairly accurate and still a bit mobile, but you'll fire later.
At very short range, like when you want to kill a Luna by being so near that he can't hit you, jump. You don't need to be accurate at this kind of range.
Lastly, if you want some CRB videos, there is a Japanese Youtuber called KT Lee. I didn't watch recently but he should be more than good enough for anyone thinking about how to play it.