blazuki
I would personally probably go for marines, with system you are bound to get noticed for fast progress as long as you put in the hard work. It's most straightforward and probable route of becoming strong. Especially because you can learn those superhuman arts and Haki. After that maybe somehow become an bounty hunter. That said as a story it's interesting see OP fic with something else than marine route :P Also going route that bring in money from the start may be better for this system, if I miss something you can get draws for money.