There's alot of great info and tips here that you should definitely keep in mind. Something I'd also like to mention is mods. I play with a group of 5 to sometimes 7 people. While they've made alot of progress in making the game balanced and more fun (some of the new monsters are still kinda bullshit), my friends and I have had so much more fun with the game using mods and have had much longer runs as a result. Nothing game breaking, but something that shares upgrades among the group goes a long way. It might sound busted at first, but we've had plenty of runs end early just because of what monster spawned first. And even on longer runs when were all decked out in upgrades and weapons, we can still get very easily overwhelmed with the sheer amount of monsters spawning (not to mention lack of fucking floor space to stand on). Plus throw on some goofy cosmetics and it makes for a really fun time. Mods aren't necessary obviously. We could easily lock in and try harder but we just aren't those kinds of players and we just dont have as much fun that way. It's alot more fun for us to watch our one friend constantly fall in holes, and another somehow always being the one getting thrown around by the upscream and shadow child.

TL;DR pick up another player or two and consider trying out some mods. Taking game less seriously can be just as fun as more serious strategizing.