Your install is not a problem. However, I don't know if you need to do the sleepers. The system can be installed under the sub-floor if access is present. In any event, I think you'll want to insulate from UNDERNEATH anyways if you go the sleeper route. Otherwise, you could lose valuable heat (and money) through the sub-floor. DO talk to your installer about his thoughts.
Bring in your hardwood for a week or so BEFORE installing so it's in a 'state' that's with that of the interior humidity and such. Also, stay away from planks because the more wood there is to expand and contract, the bigger your 'gaps' will be when it happens. I didn't look for any installation instructions but you can start at Google.com, and begin reading.