As long as you use the sim you had provided with the phone (e.g. if it's a at&t phone and you have an at&t sim), you don't have to sim unlock the phone. Also, I think c.m. 10.2 has no sim lock. Anyway, your apps and data (e.g. music, pictures) will all be deleted, so if you want to keep them, use a backup app like the titanium backup to keep them all, but if you do so, note that you have to install the app again after the c.m. setup, because as I said, all your apps and data will be deleted. As for the browser, of course you can install any other you want, although c.m. has already one.