On an iMac 11,3

A friend has an iMac 11,3. Apple no longer supports it and he has heard of me and others using Budgie, so we are considering whether we could install Budgie on it. The specs are adequate and I can’t see any problem with wiping the disk and starting again, but I would always prefer not to mess with the data.

-A very quick look look suggests that it has some complicated partitioning system with system and data partitions which appear to be one or some such strange thing.
-The file system is HFS+ (unless he has upgraded to OS 10.13) which is a journalled file system which Linux can read but can’t write to in a journalled mode, which isn’t good.
-Relocated files are also mentioned which sounds dodgy.

Would it be practical to install Budgie in the system partition leaving the data as it is? Has anyone done this who could share their experience?

I suspect that it is all so messy that it’s better to wipe the disk (after making two copies of the data of course) and start again…