I don't see a problem with what you want to do, but working out the details of each transaction will be your challenge. You may need to send more variables with the GET, and return more data from the server to the arduino and parse that out for your settings.
At 30 seconds per request, a couple dozen units should not be a problem. The exact number will depend on the server speed.
edit: I have added more code to the other thread in the link I posted above. I have the code sending a value every 30 seconds and inserting it into a database, and both are working well together. I recommend getting that working first, then go from there.