Is it better to concentrate on mastering a single weapon or to become pretty good at handling several?
There’s no single good answer for this one. Before you get an artifact weapon, it certainly helps to have some proficiency in multiple weapon classes in case you lose your favorite weapon to an exploding door or rust monster. If you go this route, practice when you’re in relatively little danger — you certainly shouldn’t wait till you find a vault full of gelatinous cubes and green slimes to figure out which end of a spear is for business. Once you’ve gotten your artifact weapon, it still might help to work on other weapon classes a bit, because there’s usually a better artifact out there to be found (unless you’re lucky enough to get crowned with Vanquisher in the Village Dungeon, or some such). Of course, very high weapon skills do grant some nice benefits, and if you’re spending your time practicing many weapons, you won’t get extremely good with any of them…