1. To unlock your phone just follow the instructions here and you'll be good to go.
http://forum.ppcgeeks.com/showthread.php?t=42503
Then, to flash a rom you just sync phone to computer and open the conflipper exe.
2. UC stands for user customizations. It's a feature that's used to install programs and settings automatically at the end of the flash process. I suggest when you get comfortable with flashing you can look into more. When you see that UC in the rom name or description that means that this feature is built into the rom.
3. I haven't heard any talk of a new release coming soon, but you can get the stock dumped rom here if you want to go back to the stock setup.
http://forum.ppcgeeks.com/showthread.php?t=42741
4. I've tried many of the other radio's available and haven't noticed any difference, but you can read through the radio thread and make the decision for yourself. A lot of mixed results, but it seems people have had the best results with the telus radio. I've flashed the radio before and after rom installs and it has worked perfectly. Never during though. You just want to make sure your phone is unlocked before you flash a radio or rom.