MSP files are update files, and are required. Don't delete.

Google earth file you can delete, but next time you use it will be created again, so not really worth deleting.

Thunderbird junk folder should be where spam is put, so you can clear that out within Thunderbird.

Within add/remove. You need to keep the updates and hotfixes, as they are mostly security related and performance updates to the OS. If you delete them, then next time you run OS update, they will all be flagged as needing downloading and installing again.

Best thing is to make sure you've run disk cleanup (or even ccleaner if you want a slightly more thorough job) then run defrag again.

As you only have a limited amount of free disk space, defrag may be struggling to work effeciently at shuffling things around, so it's a good idea to run it several times.

By far the best way of making room, is to remove any unwanted programs