get as big a machine as you can afford, not a b&q tiddler. To keep the time down to a minimum get yourself a rotary surface cleaner, these are great and dont leave zebra stripes.
On an average job, like a drive I charge about £2.50 a square meter then if you are doing blocks you add a bit on for resanding. ( the prices range I beleive, depending where abouts in the country you are. I've heard of people charging £4 -£5 psm
It is a good ad on and you can earn some good money but you need to advertise it well and it really is seasonal,