mate just go for it!!!
if you're willing to put in the hard work building a round, you'l be laughing!! i've started up twice now, first time i'd just come out the army and was looking for work and sort of fell in to window cleaning, my mum asked me to clean hers! before i knew it i had round that was paying a nice little wage, started with just the basics and soon had a van and system on the road! I had to sell up as my wife wanted to move so she could be nearer to her parents, that was almost 4yrs ago, we've now moved and i'm just starting up again. i have been driving hgv's since i sold up and just couldn't wait to get back to window cleaninig.
my advice would be, get your kit sorted first, so u can clean. then get some flyers made up. pick a date to finish work, then everynight after work get the flyers out. anyone calls u can clean at the weekend, then doorknock the rest of that street, its just about getting as many flyers out and knocking on as many doors as you can, when the time comes to finish work keep knocking every spare minute.
it does take guts to pack a job in to go self employed but a year or two down the line you'll wish you had done it years ago.
go for it!!! good luck!!!!