Hey reedw,
Looks to me that one option (without buying / implementing additional products) might be:
1) deploy the kit of all VMs from template
2) create a snapshot on all VMs (probably should do this while VMs are powered off, could script this to make your life easier)
3) do your testing. In case if anything goes wrong, you can always revert to the initial "clean" snapshot, which should be a lot faster than cloning from template again (this also could be scripted so that you revert all VMs to clean state)
4) when testing finished and you need to archive the post-test state you can either clone the kit of VMs to archive location or use any VM backup software (VDP f.x. if you have Essentials+ or higher vSphere license). Backup would dedupe and compress the data thus consuming less space.
5) revert all kit VMs back to clean state snapshot for next tests (again, should script most likely so that you don't forget any)
in case anything goes wrong with your working kit, deploy a new one from template.
whenever you need to test upgrades, restore the kit with installed old version from backup, create snapshot and go through upgrade testing process.
If all your 7 VMs always need to be used together, some things can be made easier by using a vApp - cloning and powering on/off. Unfortunately in "naked" vSphere you can't create a snapshot on vApp. Linked clones sound like a really good idea for your needs, however I'm hesitating to name any VMware products that do this now, have been away from licensing for a while.
Another option might be searching for snapshot / cloning / provisioning options on your storage array, however availability of this depends heavily on array vendor / model you use.
hope this helps!