Alltec, Prochem, Woodbridge Commercial, Ashby, Hydramaster, World Of Clean (Scorpion) Cleansmart are all suppliers of quality equipment.
A basic machine for professional use should have twin vacs at least 100psi pump (135 better) and dependant on the chemicals heat via an element on board or one which fits in line. All the above suppliers can help except the triple vac scorpion which does not have heat (but that's a whole new debate)! Machines go from £1300 up to £3000 for a new one, they pop up on ebay for around half that and include other bits of kit you will need. Some come with tools and hoses and you can negotiate extras. Most use the same pumps and vac motors unless you are looking at high volume pumps of 200 psi plus. Ive owned Alltec's for years and find they are reliable and efficent. Most others experiences of their choice seem to be the same. Of course you could go the truck mount route.
Next get some training. This often comes free with a machine purchase, which will cover the basics, or the NCCA offer quality courses which I certainly found essential. Manufacturers offer training but will focus on their range of chemicals. A misconception is it looks easy but there are so many variables for carpets and upholstery regards fibres, backings you will only get away without training for so long until something bites you back and you end up owning it.
Seek out a carpet cleaner in your area and ask to help out, you will learn a lot. We are an easy going breed happier to see a trained technician charging fairly than a muppet with a bucket trying to cut our legs off.
I also network with other cleaners who specialise and we trade customers on a regular basis when we are asked, I don't do windows or drives, but I know a man who does
Don't know about your budget but I started on my own in 1993 with 3 years on the job training after my guvnor retired with a Princes Youth Business Trust loan and grant (thanks Charlie!) for £6500 with a box trailer I think you'd struggle to do that now if you want to be serious.
Hope that helps
Simon