If you've made a good job of the planking, all you should need is a coating of epoxy resin, inside and out. Use some very lightweight cloth if you must, but I've never seen any point in it, and who wants to sand glass?
If you're going to paint it, give the epoxy a good rub down with wet'n'dry, then rub it well with a lint free cloth soaked in cellulose thinners to rid the epoxy of any of its free styrenes, which leach out of the surface to give a slightly waxy feel.
If you're varnishing do the above and then use a good spar varnish like Epiphanes. It works especially well over epoxy and is what Rivas use and Peter Freebody when restoring Rivas. There IS no finer finish
If you've made a bit of a planking cock up, then you'll probably need the glass cloth and epoxy coating to fair the hull out<G> That's OK, we've all been there, done that when time was pressing. You don't want to see my Zulu hull, before I got a coat of thickened resin on it (still no cloth though), but when I'd finished with abrasive and spray gun there sat a model that won an award in a New York gallery!
Push on!
Martin