Thumbs up for getting PBP3 Robert, you won't regret it.
As for installing it your aproach doesn't sound quite right.

My PBP3 is a payed upgrade from 2.6 and I've probably bought at least 5 upgrades prior to that over a period of atleast 15 years. My oldest is 2.31 which in turn is an upgrade from the non pro version (PBC).

In my experience there is no and has never been a need to install any prior version.

The only reason for doing it the way you describe is if you want multiple versions installed at the same time.

/Henrik.