A good book I have recommends abrading the surface with fine wet and dry. It may be that the grubby surface is skin deep and with a bit of rubbing and a bit of buffing you will be able to restore the colour and gloss, but it won’t do anything for the patch, and if it is epoxy, that really needs protecting from UV light. You will no doubt want to repair and strengthen the hull where impacts have knocked off the gelcoat and produced a star crack, white Gel-coat repair from Plastic Padding is ideal but quite a bright white.
If you do decide to to paint the hull, bear in mind that accidents happen and you will need to touch up your handywork at the end of each season. I am not familiar with Interlux but any two pack paint (like Perfection from International) has to be more difficult to patch-repair than a one pack. I am deck and hull painting a Mk2 at present and probably being too much of a perfectionist myself, but I know that my hard work will be scatched and dinged in normal use so I am using Brightside from International (now discontinued, grrrr). On a previous job I did on an Enterprise hull I used Toplac from International and four or five years on it still looks very good. Like yours that was white on white, a sensible decision. My current project (the Wayfarer) changes a white hull to dark blue. It looks great but I just know it is going to get damaged and when it does the white showing through will be very very obvious so I will want to be able to repaint it with minimum hassle.
I also agree that if you can avoid it, don’t paint the deck. It is a very complicated shape, has textured areas that are difficult to paint and even more so than the hull, will need patch repairs in the future. I have no hair left after the frustrations of trying to get a perfect finish, the final straw came when the neigbour’s cat decided to wander about on the still soft paint overnight.