Back when I was doing multiple series + retail day job I, uh, didn't sleep?
I really don't recommend that strategy.
But yeah, I work alone! :> I am the writer/penciller/inker/colourist/letterer. I do have a good friend & crit buddy who looks over early versions of the page for things that aren't clear/could be more effective, and she also gives me advice on colouring when I'm having trouble with a scene. And I get help for ASL translations from a few people and places. But the comic is created by just me!
I don't know if this is true, but it's an anecodote I like -- a professor told me about an exchange between Jim Davis and Charles Schultz, when Schultz's drawings were starting to get a little shaky. "But Peanuts is doing so well!" Davis told him, "you don't have to do this every day -- do what I do, and hire assistants to do that stuff for you!"
"Have to?" Davis asked, confused. "I get to do this every day! Why would I want to hand that off to someone else?"