135psi and 2 vacs will be fine,but if your budget will go to it then a 3 vac machine will be better.
500psi machines can squirt the water at the carpet at more pressure, I usually use up to 350-400, but you do need the means to get it out of the carpet and that is where the 3 vacs are beneficial.
Number of suppliers of 3 vac machines. Mine is a Scorpion from Solutions Cornwall - very reliable. The Airflex from Cleansmart in Nottingham, the Alltec machine from Hertfordshire, and the Ninja whilst being a 2 vac machine you can link another vac extrernally - Ashbys in Essex supply that.
Not all machines with 3 vacs are the same - its the way they are engineered that gives top performance - bit like the starting grid for a Formula 1 race - all incredibly fast but those with better engineering work the best. (of course the driver [operator] has a large input too).
The Scorpion has been on the UK market over 6 years now, is well engineered and performs extremely well.
From 2 electric power cables (which these machines have) you cannot get more then 3 vacs and a pump running at the same time.
The Alltec does have a tub heater, but as soon as you switch on the 3 vacs it switches off. SO IF you want heat, (and it is an if cause warm/hot tap water is usually available) the you go fo r an inline heater - which work better if there is a source of warm/hot water to feed it. And you dont want too hot water running thro a pump cause it will cause damage - so inline is a better bet in many peoples eyes.
Training - dont know of courses up in Scotland though no doubt there will be some. National Carpet Cleaners Association in Leicester do a 2 day course regularly which is a Friday and Saturday.
www.ncca.co.uk