I think a fresh install is a good idea. Moving the data drives should work fine as well. You might have some minor permissions issues if the new users you create have different IDs but those are easy to fix.
Posted the thread Major Upgrade Upgrade 4.x -> 5.x My approach on 4.x to 5.x - does this make sense?.ThreadServer A is running OMV 4.X. OS is on SSD. Data on 2 mirrored NAS Drives.
OMV 4.x is solid as a rock. Hardware is a dated Fujitsu Server with an Intel Core i3. Hardware performance is not an issue other than it's a large box and a little noisy.
I purchased a used HPE Microserver Gen10 on eBay and was eager to get OMV5 up and running. I have OMV4 running on another server for almost 2 years.
For testing, I wanted to run OMV5 off of a USB Thumb Drive and would go a more traditional installation…