Should I buy an existing round or build my own?

About 600 regular houses on a 4-week cycle got me to a full-time wage. How close they are matters more than how many: I only take new customers on streets where I already have three.

I went full-time at about 450, but most of mine are big detached houses with conservatories, so each visit pays more.

Yes. I bought a second-hand system in my first month. No ladders for most jobs, and you can do frames and sills on the same visit.