I went as course as 500 and still worked my butt off on the really dull areas. Then 1000. and then McGuires liquid cutting compound on a wool buff at low RPMS. I found that low RPMs worked better than high.
I'm sure others will have great recommendations on products and ways to apply, so cherry-pick the recommendation that you like and draw your own conclusions.
There is no way to know how thick the gel coat is, so you might just have to pick a not-so-noticable spot and get after it. Start course and work your way to compounding to see how well each step (finer) removes the scratches from the previous step.
While experimenting like this, always push your luck by going finer than you think will actually work. You might surprise yourself.
Based on what I see, I think you should try another step courser. Courser can level out stripe edges better than fine. Courser can save you a ton of time if you find the ideal grit.
The courser you go, the more steps you will have to go through to get to polish, but on the other hand, if you try to do it all with paper that is too fine, it could take much longer.
Use some Dawn dish soap in your sanding water as a wetting agent and to reduce drag. Your arms will thank you. Dip often to keep the paper from clogging.
