Well, i suppose this is more like research, since I'm planning to get the '10 Mac Pro sooner or later.
You'd need an adapter to use internal disks, available at MaxUpgrades (
here).
That said, I'm only really interested in RAID 5'ing the internal drives. External ports would be a plus if i ever end up doing that (although I somewhat doubt it). So just one external would do (assuming it supports PM, again, if i ever need it).
You can take an internal port externally via the correct cable (
SFF-8087 to SFF-8088). The other solution is to use a hybrid card (both internal and external ports;
example &
price). There are fewer such cards though, and getting an internal port card (2x SFF-8087 ports) would be cheaper, such as the Areca
ARC-1222, and use the cable linked (it gets run out of an open PCI bracket, so you'd lose the use of a slot, unless you're willing to cut a hole somewhere on the back of the system).
Both of these cards can boot OS X (but only OS X or Windows/Linux, not both, as the firmware can only contain EFI
or BIOS). But if you install the drivers for another OS, it will still work if the firmware isn't correct to boot it (i.e. boot OS X, but will run under Windows/Linux once the drivers are installed).
Either of these cards is more than sufficient for what you'll be doing with them from what you've posted (both use the same 1200MHz IOP processor).
Intending on using HDD's. OS X. Don't think i'll bootcamp windows, but id like to keep that option in the future.
You won't need Boot Camp, as it's just a partition tool (can't share the RAID set with mulitple OS's). You can create multiple arrays on the card however, and go that route (but it won't boot both OS's; see above).
The way around booting is to use the SATA controller in the system to boot a separate Windows disk (i.e. toss it in the empty optical bay, and attach the cable).
Please understand, when using a proper hardware RAID card, you'll need to run enterprise grade drives (both of the cards linked are SAS models, but they also run SATA). But if you try to use consumer models, the array won't be stable, even if you do get it to initialize (the recovery timings in consumer models aren't suited for RAID; consumer = 0,0, while enterprise disks = 0,7 - numbers are seconds for read and write respectively). You can't change these values on consumer WD drives any longer (other brands haven't had this option at all).
I just wish there was software RAID 5 in OS X, cause I'd be content with that haha
No you don't, as software based implementations aren't suited for pairity based arrays (you'll end up with corruption at some point), as it doesn't have an NVRAM solution to the write hole associated with parity based arrays (levels 5 and 6, and carries into nested levels 50 and 60 = 2x parity arrays - 5 or 6 - then stripe both sets together).
You'll also need to run a good UPS for power protection (preferably an Online type). Batteries exist for some cards, and ideally, is a good thing to have in conjunction with the UPS. But not all cards actually have them available (i.e. ATTO).
But of course, cheapest would be nice.