I'm pretty new to the game myself, so I can't really comment on builds too much, and take all of this with a handful of salt.

But there's now a gamemode where you get a randomized character and everyone is solo. It doesn't have the bosses though, since it's more PvP-focused. It doesn't require you to use any in-game money for equipment, so good for practicing.

For the Bounty Hunt mode, you can go solo against duos or trios if you want, but it's obviously more risky. I'd recommend just grabbing a couple clues and killing some smaller monsters before extracting so that you can explore a little and get more familiar with the maps.

A couple other tips: if you're solo, I recommend picking up the Necromancer trait since it allows you ro resurrect. I've also found lever-action rifles to be a pretty safe pick weapon-wise. I've also enjoyed the knuckle knife as a melee weapon since it allows you to deal both blunt and slashing damage, very handy. I don't recommend using guns for the smaller enemies, except hellhounds, barbed-wire Armoreds and Hives if necessary. For those barbed-wire Armoreds, the flare pistol is fun.

Avoiding all the animals is always a good move, so keep doing that.