So looking through the various firearms already found on DND Beyond, I’ve decided to go with the firearms under the Critical Role content Gunslinger Fighter subclass in priority to the DMG firearms (although those firearms may become available later in the campaign).
Here’s the DND Beyond link to the Gunslinger subclass.
For quick reference in our campaign, they are as follows:
Regarding reloading, the Reload property shall use the action economy given in the DMG.
Characters can replace the starting equipment ranged weapon option (such as javelins/crossbow+bolts) with a pistol and 20 rounds of ammunition.
Firearms in this game are enchanted to produce the propellant, to craft ammunition you only need to create an appropriate projectile from metal. This also means that firearms don’t need special measures to keep powder dry, etc.