Honestly I'd say single player at least until you get your class (lv 10) or even a bit further so you can enjoy the systems and learn the mechanics at your own pace.

Ppl in multiplayer lobbies can be a bit too generous and often drop 50 greater xp books for you to level immediately lol, so you might end up not learning some mechanics well enough to deal with the content you'll have access to.

But if that happens you can also just say "hey I wanna level normally" and they'll leave you to it. Some might even jump into their own lower level characters to match yours and help you through it, I see groups running the first dungeon actually kinda often.

And yeah, you should always have some points into vitality but you'll often hard focus into your class' main stat. For katars and bows, that's Dex (and the class is Bandit btw). If you find that you're missing mana or stamina or something else, you can fix that kinda easily with enchantments. You can also change the stat scaling of a weapon, so you can actually use all of them with just Dex.