Purchased a Nexus S, have a few questions

I've had an iPhone 4S since launch, getting kind of bored with it. I was looking into getting a Galaxy Nexus, but to save money I decided to buy a Nexus S and keep my iPhone as a secondary phone until I decide what platform I prefer. I just have a few questions.

1. The phone I purchased is supposedly running a custom ROM. I know ICS was recently released for the Nexus S. How can I install plain ICS?

2. The phone is rooted. Is this potentially a security risk? Is there a way to disable root access completely? Any tips about this would be great.

3. What's the best way to set up remote wipe on the device. Apple has Find My iPhone, does Google have anything similar? Is it safe to use a third party service to remote wipe the phone?

4. And last but not least, tethering. I have an unlimited plan on AT&T, is there a way for me to use a tethering app without getting in trouble with my carrier. Any tips on tethering apps?

Any tips would be greatly appreciated.