Honestly I feel like early pistols will be relatively common, they're a staple of the pirate genre after all. I mean think about it, which is more iconic, a badass pirate with a brace of three or four pistols slung across his chest, or a badass pirate with a bow over his shoulder and a quiver of arrows at his side? Which reminds me, as far as multiple shots, it was common practice for pirates to carry multiple loaded pistols when going into a fight. The reload time may have been slow, but they could still get shots off at the speed of an archer until their guns were empty, and at that point they would usually just switch to melee weapons.

Also, keep in mind that it's a setting with magic. It would be more expensive, but you could totally buy pistols that had enchantments on them to protect them from failing due to water. That's the kind of basic enchantment that would be so useful that there's no way it WOULDN'T get developed.