Sorry I missed this. October was “hell month” for me. November is slowly calming down. This fell through the cracks, I’m sorry.
You missed a few models from the NAS Compatibility Guide
– DS220+ (2-bay J4025)
– DS423+ (4-bay J4125) – MUCH BETTER and adds two bays of future proofness
– DS224+ (2-bay J4125)
You’re looking to future proof. I would add the extra bays NOW. Upgrading the whole chassis later is expensive.
Upgrading to DSM 7 is well defined (has been for quite some time now). As long as you don’t panic and start deleting things, everything can be migrated from DSM 6 → DSM 7