I think it may have to do with the command name and file name for the boot img. Instead of "fastboot flash recovery recovery-Tiamat-R4c-100611-1150-cwm.img", I beleieve it would be "fastboot flash recovery recovery-solarnz-100611-1150.img" for the most current of the R4c recovery. It seemed to do the job for shyyour with the file and command I supplied. That's what I think.
That's great to hear that's it's back! Here we go...
1. A Rom is the entire system itself as a whole, meanwhile the kernel is more specific to the processor especially, and other lesser things such as the Wifi module, charging light, etc. I would advice you to use both a custom Rom and a custom kernel if you want the most performance and battery life out of your Xoom.
2. Hmm... some of these problems sound kind of serious. Not sure how to go about the Gmail account issue. I can advice to you stay on your current Rom and do a complete data wipe, cache wipe, as well as a dalvik cache wipe from within the CWM Recovery. Be sure to keep that Nandroid backup just incase, and backup all of your apps with their data only via the Titanium Backup app. A clean new install of the current Rom should remedy most if not all problems. Don't forget: Never restore or backup the system apps, as if there was a problem with them before, restoring them would bring that same problem right back to the new install.
If all else fails: Report back here with any other questions or concerns.