I use Windows 7 on my laptop as well and everything works fine. You
'll be able to unbrick as long as you can go into boatloader mode(holding up on d-pad and pwr on) and flash the stock sbf file using RSD lite.
The ROM really has nothing to do with the prl. You can use a stock ROM and Kernel and be good. The only purpose of the ROM would be customization. And if your planning on changing the ROM, make sure that it supports IP Tables for the simple fact that you need them if you want internet and mms. The stock ROM and Kernal supports everthing needed.
If you go into settings/about phone what does it say for the PRL(all the way at the bottom) thats on the phone?
The latest for Metro is 2004 but you get that once you update your roaming list by dialing *228.