AwAcS
Recruit
The processor for M920x tiny i5 9500t is adequate and so is the Ram (for start). What you would end up having trouble with is storage in terms of mini pc. For setting up RAID it is advised to have the storage of same make and model. What you can do is boot proxmox from a 2.5 inch SSD and place 2 X nvme storage in raid.
Considering that you would want to offload all you cloud data here, Nextcloud would do the trick but then, the storage limitations would remain. Hence, you can also look into sff providing same specifications and future upgrade path as they also would have 2/3 or more sata ports. These would also provide you with decidated pcie and in some cases, multiple pcie in case you want to add network adapter or GPU.
Considering that you would want to offload all you cloud data here, Nextcloud would do the trick but then, the storage limitations would remain. Hence, you can also look into sff providing same specifications and future upgrade path as they also would have 2/3 or more sata ports. These would also provide you with decidated pcie and in some cases, multiple pcie in case you want to add network adapter or GPU.