RAID 5 on PR4100 w/3-drive RAID and 1 JBOD?

I’m not very familiar with setting up any RAID, though I understand the concept.of striping. What I’m not confident about is how the PR4100 device would or does treat the drives installed to it.

I’m considering buying a PR4100 w/4 X 8 TB drives, and having RAID 5 across 3 drives, e.g. across drives 1 thru 3, and keep the 4th drive as a separate (JBOD?) share/drive, i.e. not part of the RAID. I don’t want/need the RAID to use all 4 drives.
I understand that will limit me to 16 TB of storage, but am hoping it would also allow for swapping out drive 4 without affecting the RAID. (I’ll be using external USB 3 drives on the rear port(s) to store backups).

Does the PR4100 device and Dashboard/setup software/firmware allow that configuration?
From reading the User Manual it appears to, but I haven’t been able to find info that clearly answers my specific question in a manner that my simple mind can comprehend.

Sincere thanks for any feedback.

Yes, you should be able to create the RAID 5 with 3 drives and then add the 4th one to the unit and set that as JBOD.

could that 4th slot be used for an Read/White SSD Cashe drive?

Also if i buy a Diskless and add 3 6tb drives doing raid 5, could i add a 4th drive at a later date with out dataloss and add to existing raid array?