Belt - I would pull it and clean it with mild soap and water and inspect it. If there are no signs of heavy glazing or chunks missing, by all means go ahead and keep using it. Ideally, if you don't have a spare, I'd get a new belt and keep that as a spare, but that can wait until you get it fixed up and running reliably.
Axles - I would trust Tusk to be as good as stock, but I would recommend SuperATV Rhino 2.0s if available and you're going to spend the money. Again, I wouldn't invest in these upgrades until you get it running reliably first.