As already mentioned, recommend deferring wingtip fit up until after the wings are on, and you have the flaps and ailerons perfectly rigged.
As far as filling in the exposed ribs, this is a builder choice. On both of my projects I filled in all such voids (flaps, ailerons, wingtips, elevators, HS and VS). I used a piece of rigged foam glued into the rib with micro. I left a 1/8” or so gap between the foam and the rib sides. I then added a couple of bids of glass on top of the foam with the glass edges pushed down into the gaps. The glass is about 1/32” or 1/16” below flush with the rib sides. After cure I add a thin layer of micro on top then sand. My thought was just putting micro on foam would crack as micro has no strength.
One other tip, use a small straw at the apex of the rib to create a water passage so any trapped water can get out.