Repository sizing recommendations?

Hello,

We are now up to twenty 2TB repositories for vRanger.  I had earlier mistakenly thought that moving to GPT disks for the repositories would prevent us from doing file level restores, but I see that was not correct.  Having GPT disks in the VMs prevents FLRs. 

I am now inventigating combining some of these luns into larger ones to use the repository space better.

Is there any published list of best practices for repository sizing?  Does anyone have any personal stories of what worked for them and what didn't?

Any help would be appreciated.

Thanks,

Greg