I traded for a mac; how can I change the home folder name?

Trying to address some of your questions:

You state you are running Mountain Lion? Was that the original OS on the Mac? That is very important because:

a) if it was, the seller/trader needed to transfer the Mountain Lion license to you or it will stay with his Apple ID;

b) if he purchased ML, he is required to uninstall it before selling the machine because the license is not transferable, which means - again - that it is tied to his Apple ID (along with the machine ID).

Both/either can present some problems for you since ML is now tied to someone else's Apple ID. If you manage to "introduce" your Apple ID, it will no longer match the records MAS (Mac App Store) has, so updates or other purchases may present problems.

I would suggest that you either call Apple or book an appointment at the nearest Genius Bar and ask them how to proceed - that way you may be able to set up your own Apple ID on the machine as well as get ML registered as yours (although, as explained above, they may require you to purchase it for yourself).

Whether or not you made the right decision - well, I've never owned a Windows machine, so I can't answer your question since I have nothing to compare it with. Obviously, I use Macs...... you should be able to run your own test: just do what you normally do and see if it appears to take about the same time, is faster, or is slower.

https://discussions.apple.com/docs/DOC-3872

Out of curiosity, what would happen if the OP changes the name and then tries to update apps/OS or check the OS purchases in MAS to redownload (or use the recovery option for that matter)?

Ok, so you purchased ML, so there is no problem there...... have you followed the instructions in baltwo's link? FWIW, the home folder user name is the name the computer was set up with originally. I've read of one possibility if you want to try this (have not tried this myself, so not sure if that'll work): create another user account with your name and full admin privileges, login password, etc; after you've logged in as that new user and you're satisfied that everything is working as expected using that account, you could simply delete the old admin account.

http://support.apple.com/kb/HT3309

Glad to hear that worked and thanks for the feedback!