You said you tested different mice but they were both PS/2, right?
Can you test with a USB mouse?
A long shot, but maybe it's a PS/2 problem with your motherboard.
I understand about "a real pain to monitor every single program"...
That's why i suggest creating a backup image after getting Windows updated and before starting to install your programs.
That way you can restore a "Clean Vanilla" OS if a program causes problems.
You could also install your programs in "Groups" instead of one at a time and test them.
Install perhaps 5 at a time, and do some testing.
That could narrow it down quicker if a program is the issue.
When i build a new PC, that's my approach.
I may create several images per day initially, and re-install Windows more than once to get a clean "start-up point".
It is time consuming, but to me it's worth it to know I have a clean install image i can depend on and restore.
As far as security, you will get many different opinions.
There is a SF "System Security
" sub-forum you can take a look at. System Security - Windows 7 Forums
It has a sticky you should look through. What's the Best Anti-virus?
IMHO the most important part of security is the user.
- use torrents, visit dodgy websites, open unknown emails/links, etc. ???
- No security program is 100% at preventing viruses or malware.
There are many free anti malware programs that are recommended and well regarded.
I suggest Malwarebytes free for on-demand scanning.
Personally, i use the paid version for the real-time protection.