You are not a newbie to carpet cleaning.
Now with experiance, and particularly if you have a good budget, I would personally jump to a good portable, skip the intro machines, you been there and done it (although nothing wrong with them and if budget is an issue then go for one).
Because of personal experiance I can recomend the CFR500 Pro and the Scorpion. With the hoses, wand and hand tool you will need, both will come around or above the £3k mark, but go for a deal as a package.
As Paul King said - find a supplier that will let you have a go, or a friendly owner somewhere near to you (Swindon is it).