I have seven 24v 2amp thermostats. Do I just need a single 24v 2amp power supply to power them?
That will adequately power the thermostats alone
The full spec page for your Tekmar 532 thermostats states they need a power supply of only 1.8VA for themselves.  Since your power supply has 24V * 2A = 48VA available, you can easily power all 7 of them, leaving 35.4VA of capacity left over.  The 2A spec is what the internal relays are capable of switching; i.e. your connected devices must not draw more than 2A.
Now, keep in mind that your transformer needs to power both the thermostats as well as the devices they control, and the devices sometimes have larger power requirements.  If your devices do have large power requirements, you may want to use separate transformers for each thermostat, or one much larger one.  It also doesn't hurt to oversize the transformers a bit, since they will run cooler and last longer that way.