When you root the phone you are essentially erasing it (except for the SD card) so you need to back up apps using another program like titanium backup backup to your SD card. Just backup the apps not the system settings. I’m not sure on doing a full Rom backup as I have yet to do one. Personally I just downloaded the Verizon rom zip file from the XDA in case I had to put it back on the phone.
Make sure the Rom your flashing is for Oden and not CWM. A lot of the Roms file options give you two versions. I have only used the Oden Version personally.
In answer to your question Oden does not make a backup of anything it just loads the rom for you. I personally did not do a backup the first time because I did not really understand how to do it at the time. Fortunately it all worked out. Now I use Titanium to do backups for my apps to the SD card. I have read that if you go to the settings->About phone-> System updates the phone will install the latest Verizon stock rom and remove your root access. So if you needed to your phone would be back to normal. I have not tried this because I haven’t needed too. I hope I never have to return to stock.
I believe there is a way to backup an entire ROM you will have to check the XDA forums or this forum. There is also additional information there or maybe an even easier explanation on the process. I’m by no means and expert or anything but on XDA most dev’s provide installation methods or at least links to how to do it. If you get stuck just post a question to Dev who’s rom your trying to install.
I personally did a lot or research before I felt comfortable rooting the phone as I didn’t want to brick it. I followed the instruction step by step and had no problems at all. Just have to be patient.
Hopefully the humble 1.6 Rom will be out tomorrow or Wednesday then you can down load the zip file and flash it. And enjoy better battery life and speed with no Lagg or bloatware. I will be doing the same.
Just remember flash at your own risk!