Welcome, you have found the best place on the net for these little dudes.
Stock software on the server you can use 4 (2tb) drives.
The system does not use a typical raid setup, it has a main system drive with a OS partition and what is left and all the other drives are pooled into 1 large drive.
Forget the mac, the older versions of mac worked but the newer version is not supported.
Win7 32 and 64 bit win 8 and win 10 are all still backing up and working.
I use all red WD drives 2tb, they are not as fast but do run cooler.
Some use WD blacks for the speed but they do run warm.
The system sets up defaults folders for Music, videos, user folders, photos.
Hope this helps. Read some of the guides.
Two things:
1) when you get all setup and have all the windows updates and all the HP updates then go out and get the Free Smart addin to keep and eye on your drives.
http://www.dojonorthsoftware.net/dl/InstallHomeServerSMARTClassic.zip2) always have a backup outside the server of the stuff you can't lose, because the server runs Windows and we all know that things can go very wrong very fast.
Some backup to the cloud or external drives, something. I backup to another server. and to other drives.
As far as upgrading, you have the last in the series of this Gen of micro servers, hardware wise. The EX-490 and X-510 were the last of the systems running the stock software. The ram and the cpu can be upgraded if needed. The stock software is win server 2003 and is End of life, but still usable IMHO.
Some but the video adapter and install win server 2011 which is built on win server 2008 and some have installed win server 2012E.
If you upgrade to these OS'es the hardware can run larger drives and these OSes are 64 bit. The stock software is 32 bit, hence the 2TB limit.
I plan on using mine stock for as long as I can and I will pass on Win 10 for now and wait a couple of years to see what happens. Win 7 works fine for me.
I have 9 win7 PC's that backup to the server and 1 vista PC.
You should be able to map to any folder for devices to find your data.
One of the best things I like about these little servers is you can pull any drive out and attach it to another pc with a usb to sata dock or cables and you can read your files.
Most NAS'es can't say that.
Good Luck and as you get farther down the road, shout out if you have questions.
P.S. ram can be upgraded to 4 gig in two slots.
The bottom bay is the system drive bay, that drive always has to be in that bay, the other drives can go into whichever.
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[X510 CPU/RAM/
All 2 TB Red's] [X510 CPU/Sync'ed Backup/All 2 TB Hitachi's]
[X510 /2 in box]
[X710 LIAN LI DIY W2016E] Stablebit Drivepool [EX-503 LIAN LI 5-bay USB3 External]
Fear the Cloud