Initial Hard Drive Set Up With UNAS Pro

I am thinking of getting a UNAS Pro, so just wondering how it works with adding drives.

I doubt if I will ever fill all 7 bays

I was initially going to use 8TB, but that would only give me 43.6 TB on the 7 drives.

However, if I use 16TB drives I could get the same amount of storage with only 4 drives.

Is there an issue with only adding one drive at a time?

I was initially going to put one drive in and get the system set up and used to how it works and store some initial data on there. None of this is critical, so if the drive failed I can replace the data.

Will there be a problem adding one drive first and then a second in maybe 6 months time and then the 3rd in about a years time.

This way the drives will have different ages on them?

When I add a second drive, I assume this would become RAID 1, will it automatically change to RAID 5 when adding a 3rd?