Great story! Glad it's not your typical OP from the start MC. He starts off really weak but is progressing at a nice pace. Also cool that he's encouraged the rest of the crew to train more too. Particularly Nami and Usopp. They've got so much untapped potential that is literally waiting to burst out. Only thing that I've found a bit iffy, and they aren't even too big, is 1. Why's bro keep calling Luffy captain? Like, I get he's your captain, but he's also your friend. Call him Luffy in normal situations, but call him captain in serious ones. And 2. I feel he's giving out too much information. I know he's set up a background where it would make sense, but that background is a pretty weak one which could be easily popped, and doesn't explain why he's knows so much about certain individuals. Some things I suggest for your story, which aren't really too involved with your character as I like him. 1. Add onto his "backstory". 2. For close combat, when you reach Skypeia, have Usopp implement dials into his Hammer for close range. Maybe also have him get those bouncy boots from the Shandians (Can't remember too well, it's been quite a while). 3. Make them spar and learn off each other. By now I feel at least Robin, Franky, and Brook should've unlocked some basic haki. We've got 4 masters of it on board the ship now, there aren't much excuses. It would be cool if SH were like a Rocks second coming, although on a much smaller scale. Where all the Strawhats in their prime are atleast 3rd Commander level. And last 4. Please add in some wholesome canon chapters. Where it's not all about plot, and it's just the crew getting up to their same old shenanigans. That's all from me, sorry for the word vomit. Just wanted to get across to you how good your story is and possible things to consider. I know you've already gotten a lot of comments on it, and you've already responded, but I just wanted to emphasize how much you can't drop.
Thanks!