Adding drives to Raid 6..does it matter if I already have data or not for speed and "safety"

Hello,
I have a RAID 6 setup with 5x8TB drives. I havent transferred my data to it yet. I was wondering if it matters at all if I transfer the data now then add 3 more drives later of if it will be faster to add drives if there is no data yet?
Also, I guess when adding drives, it will be best to add all 3 at the same time and not one by one as I buy them?

Thanks!

All of this depends on the raid implementation. For linux software raid it will take the same amount of time regardless of how much data you have on the array. Adding all 3 at once will be faster than adding 1 at a time and waiting for the reshaping to complete before adding an additional disk.

Thanks guys. So looks like my best path is to add the data now but wait until I have the next 3 drives to add them all at the same time.