As rob has said, I very much doubt you will make a living from this, gutter clears are a one hit wonder, windows is every 4/6/8 weeks depending on your set up.
The father in law tried this 5 years ago, threw loads of cash into getting a vac, then loads more in flyers, advertising etc... Couldn't scratch a living from it, at that time we had a small (around 350) customer base from window cleaning, offered this service and got a good steady flow of work, 4 years down the line with advertising and over 1000 window cleaning customers it's an excellent add on service that brings in a decent amount of cash flow.
Gutter vac'ing on your own is also quite tough, we vac as a pair, cuts the time down by over half over a single operator
Darran