I'd be more inclined to start from scratch moving from Eclair to Froyo. You'll find the file structure changed a bit, directories and files left behind. No need to re-flash, you just reset & clean it all including re-format the internal SD from the recovery mode. Just back up any important data first, sync the apps and reinstall afterwards.
Flashing with Odin is very straight forward, not much to it really. Although if you do decide to start flashing ROM's etc, which can be very rewarding grab a copy of the /efs folder, all the important signature files are in there, but you'll need to root it first.