Looking for advice on array structure/disks used

I recently purchased two 12TB drives to upgrade my array.  1 is now my parity drive, and the other is now an array drive.  I currently only have 10TB of data, so the new 12TB drive will hold everything, for a while longer.

 

I'm not sure if I should remove all the other drives, and just use these 2 drives for the array, or leave the other drive(s) in for some reason.  I can always add drives back if/when I run out of space.

 

I'm wanting to move the server parts to a much smaller box than what everything is in today, and I need to get down to 3 or fewer (3.5") drives, to fit the case I already have and wish to use.

 

Is there any benefit to keeping a 3rd drive in the array, or is it "just as good" to shrink to only the 2 new drives (parity and array) bought on the same day (same brand, type, etc).

 

If I do keep another drive in there, which of these should I keep?  (I'm leaning to the 7200 RPM that is only 2 years old)

 

Disk 1 - Model family:Seagate Desktop HDD.15     Device model:ST4000DM000-1F2168     Rotation rate:5900 rpm     Power on hours 50578 (5y, 9m, 6d, 10h)

showing no errors under attributes

 

Disk 2 - Model family:Seagate Desktop HDD.15     Device model:ST4000DM000-1F2168     Rotation rate:5900 rpm     Power on hours 54367 (6y, 2m, 14d, 7h)

with a Reallocated sector count = 40 and Reported uncorrect = 11  (errors?)  highlighted in yellow

 

Disk 3 - Model family:Seagate Desktop HDD.15     Device model:ST4000DM000-1F2168     Rotation rate:5900 rpm     Power on hours 46364 (5y, 3m, 14d, 20h)

with a Command timeout = 10 11 11 and UDMA CRC error count = 4546  (errors?)  highlighted in yellow

 

Disk 4 - Model family:HGST Deskstar NAS     Device model:HGST HDN724040ALE640     Rotation rate:7200 rpm     Power on hours 18951 (2y, 1m, 30d, 15h)

showing no errors under attributes

 

Finally, should I even keep the disks with over 5 years and errors, or empty and trash them?  What about the 5 year old drive with no errors?  Worth keeping as a backup for something else?

 

I appreciate any feedback or suggestions.

 

18951 (2y, 1m, 30d, 15h)