Re: bottom paint
Very confusing question ( to me anyhow ). You say you've sanded down the old paint. Was it antifouling paint or something else?
The way I see it you can pretty much do anything you want from there. Repaint, leave it - just depends on how you want it to look.
If it is antifouling then go back with the same. If something else go back with "something else".
And no - as far as a clear coat is concerned it makes no sense to do that. Gel coat is a process that you do not want to get involved with - forget that.
As TheWoodCrafter mentioned - your answer would be helpful to determine what type of bottom paint to reapply - if that is the way you want to go.