Overtop,
Just Flash the firmware not the eMMC. That way you retain some of your app and various setting such as contact, email, 2 desktop screens etc. Once you got your phone where you want it to be, do a backup and save a copy on your PC.

I believe someone mention that you should manually turn off your N900 BEFORE it do the random restart 17 or 27 times. (I believe 17 times) That way you won't get stuck at the loaded screen.

There is a temporary fix for the random reboot by changing some number from 0 to 1. Check the reboot thread for the quick guide to.