HTC Eris :: Flashing/rom Upgrading Safety

I recently got rid of my iPhone (couldn't stand Job's arrogance anymore) and decided to go with the cost effective route of MetroPCS. When I found Android phones could be flashed to work with it, I was quite excited. I found a phone and someone to do the flashing on Craigslist (actually a local phone shop that does it).

He flashed my phone and loaded Evil Eris onto it. I wasn't under the impression that if he put this rom on, I was going to have issues, like no voicemail notification or softkey leds. Going into this, I was pretty unaware of all the different rom choices, and the effects they have on the phone, and I still kind of am. So I have a few questions, because I've been reading about Ivans and kind of want to try it out, but want to make sure I've covered all my bases.

1. I am still unaware of the exclusivity or co-dependence that "flashing" a phone and changing a rom have with one another. He flashed my phone to work with Metro, and upload the Evil Eris rom. Main question is - if I wipe and load Ivans, do I lose the ability to use Metro? Or is it simply an issue of loading up my Metro APN (i think thats right) settings once I've loaded the new rom?

2. Nandroid backup - I made one the other day. If I go in, try another rom, and screw something up, I am under the impression that I could restore that backup and my phone be working like I never left it, including MetroPCS settings, correct?

3. Can anyone suggest a good program to backup and restore carrier specific settings, so that if I load a new rom I can quickly port settings over? Does something like this exist?

4. Finally, if all of this has been answered somewhere where I didn't find, feel free to send me to those links!