Bill,
I was window cleaning for 12 years and made a slow transition to carpet cleaning, with them overlapping by about two years.
This gave me a good time to build a good customer base and still have a steady income, which is what keeps you going.
I intended to keep both businesses going but you soon realise that you dont have time for both if working alone, plus i was making double c/c than windows !
You are in a good position to start c/c as you are already self employed, obviously have transport and use to being your own boss, also as stated have a good customer base to market to.
I would say go for it - the only thing i regret not doing at the start is getting some good training, as not only does it point you in the right direction but gives you the confidence to do the job as well.

regards
steve