Set up for use with both PC & Mac

Just purchased a drobo gen 2

looking for some suggestions on a set up for my home
Going to be used for Mostly back up for my Mac
But would also like to use as a PC back up

I have not set this up yet but I am starting to understand that it may not be quite what I expected. I was looking for a NAS that I could access through my network from any computer on that network

How should the drives be formatted ?
If I choose to use this as a mac only and set it up as HPS will that limit the use of plex or any other draw backs I should consider?

Sorry for the Nube questions