Steve
Just looking at your original post.
Interesting the order that you listed the types of carpet. ie "floor tile carpets, general grade commercial carpet and deeper pile that you may get in homes?"
If that is relating to the quantity of c/cleaning you perceive you will be doing then I would start off going down a rotary machine route.
This can be done fairly cheaply. Good news eh!
Get a 2nd hand 17" rotary, max 220rpm, for about £200
Pads for it are more difficult to pick up 2nd hand so may have to go for new at £18 each (may need a lot - ie 20ish)
Get a very very good upright cleaner - Sebo BS36 or a 2nd hand Kirby (yes I am serious).
An 8 or 10 litre sprayer - stainless steel preferred, last ages, buy cheap-buy twice.
A little spotting machine, may get one on ebay for £150-200. This is to remove spots via water extraction which obviously rotary cannot do.
Bit more stuff maybe and away you go.
For cleaning carpets in homes, defo go down the hot water extraction route, at least twin vac 150psi ish.
but you can make lots of money in commercial sector if you prepared to work "funny" hours - nights, weekends etc.