-Is it possible to install e. g. Framework 3.5 on client that has only Framework 2.0?
Yes, you can do this using software distribution. This is set up in your scan template. To see how to set this up I'd suggest looking at the following help document within Protect:
-What is the difference between Security Patch Scan and WUScan?
Security Patch Scan only scans for security patches (including 3rd party), and WUscan will scan for both security and non-security patches.
-How many clients are supportet in the evaluation?
I believe it's 50 seats for the trial version.
If you are just getting started with Protect it may be helpful to check out the training videos available here as well:
I hope that helps.