Older version of flash will not always function on some sites, and the latest versions require more hardware grunt

When you install things, even from known trusted sites these days, look carefully because they may have by default ticked that you accept having your home page set, etc

Thats not to difficult to change. New tabs function should able to be changed in the browser

If you want your old version back a recent restore point  may do it, assuming you dont know which version you previously had

No, it wont erase your files, though some things may change position depending on how old the restore point is and what you have changed recently.