Anything is doable. I bought a business that had already been around 25 years and all new equipment to the tune of around $75,000 and know I didn't have much over $1,000 in the bank at the time. It's about like any business, the first 5 years will make you or break you, but I survived and it's been a good thing in my life so far.
I've got zero motivation to go out and knock on doors, and I hate it when people come by trying to drum up business wasting my time when I didn't call them to come by so that's probably why I have no ambition to do that. That's the reason I bought one that had already been established in the community. It costs more out of the gate, but I knew I'd have some sort of flow of work coming in w/o doing any advertising.
I'm with everyone else, sub stuff out till you make sure it's going to flow for you. The internet wasn't what it is today when I started, and I didn't have all these great options we do now. You either did it in house, or you didn't do it on most jobs. Now, when I get busy, even I'm using those subs to keep up, and it works great.