Hi Seamus. Several things...
Firstly the HD will do a damn good job on the majority of the soiling, so not a bad choice at all. I'd dilute it at 1:20 or maybe even 1:15 for this job and apply it as hot as possible. Yes it does need agitating the same as any other product but not any more than anything else. It is the type of carpet and soil conditions that determine the agitation needed, not the product you're using.
However if it doesn't cut the mustard on certain areas it would be wise to have something as an alternative like powerburst. Each of them can be better than the other in certain cases, so it's good to have a choice. However you obviously can't go shopping before the job now, so hopefully you've got a few options chemical-wise.
If you have an oxidising additive I would use it regardless of the main pre-spray, you should find it helps out a lot.
Choice of attachment for the rotary: Presuming it's the usual type of pub/club carpet (contract axminster or similar - cut pile) a brush attachment is ideal but if you haven't got one, the carpet bonnet will do a much better job than any of those other pads you mention.
As far as practice goes, have you got a smooth hard floor at home? (e.g. tiles or vinyl) If so, stick the bonnet on the machine, wet up a couple of square metres of your tiled floor and have a play with it. As already suggested, you should concentrate on setting the handle the right height - I find it right when the handle is around my belt buckle height (you should too as long as you don't wear your trousers like Simon Cowell

)
After a little practice you should be able to control the machine with one hand, out of the corner of your eye whilst texting on your phone with the other hand

When you move on to carpet you'll find the friction much greater, so it will be a lot more difficult to control. But if you learn on a nice smooth hard floor first you'll be able to cope with the carpet much better.
If this wasn't a nightclub or similar I'd probably be advising you not to try the rotary on a "real" job without experience, but in reality there's probably very little danger in this case.
Have fun
