T7400 RAID Configuration Question

I have a recently acquired an original-equipment Dell T7400 workstation dating back to about 2008, and am in the process of upgrading components and software to make it a quite decently performing workstation and personal server. The work that I will ask of it will include software development (mostly Visual Studio), graphics file transformations (e.g. VOB to mp4 via Handbrake), some light SolidWorks duty, and file/device sharing in a small network. For aesthetic reasons I am interested in transforming it at a modest cost that would deliver high value for the dollar, and would like not just opinions on the chosen upgrade hardware but advice on possible RAID structure for speed and redundancy.

The system appeared (discovered in a recycling dustbin, believe it or not, as I was dropping off an elderly machine) with A08 BIOS, a single E5405 2.0Ghz processor, a mismatch combo of 2 x 1GB and 2 x 2GB memory sticks, a single 80GB drive on the SAS controller, an NVIDIA Quadro NVS290 display board, and Vista for Business. And given that the motherboard is dated (0RW199), there are only 3 PCI-express slots, with the remaining slots primarily the dead-end PCI-X.

I removed the 2 x 1GB memory, flashed BIOS to the latest A11 version dated 2012, and installed Windows 8.1 with a Windows 10 Pro upgrade on the docket. It has surprised me that 8.1 is a decent environment, as long as the dreaded panel environment is avoided. (Let me recommend IOBit's 'Start Menu 8' as a good way to bring back Win7's look and feel.)

To bring the system up to speed hardware-wise, some well-priced new-to-me parts are winging their way here: 2 x L5420 2.5Ghz low-power processors (if not the L series for operational efficiency, then some X542's 3's, 4's or 5's would have been chosen); and 16GB memory a in 4 x 4GB format (that leaves 2 x 2 memory slots open if I want to go to 32GB in the future). For a graphics board, an AMD/ATI V4800 workstation board compatible with SolidWorks is on its way here. The total of these, including fan/heatsinks for the processors, comes to less than $120 (I am almost embarrassed to say), so if any of them comes a cropper the configuration can be altered with little lost investment.

With the processor, memory and graphics components considered completed, I turn now to the question of disk configuration, where speed is definitely desirable but safety need be paramount. My thought is to use the on-board SAS controller, which as I understand is restricted to RAID 0 and/or RAID 1 options. There is a max of 4 disks on the SAS controller, and I am thinking of setting it to host the 4 disks as 2 pair of RAID 0 disks, in which the SAS hardware/firmware controls the RAIDing. But then these two pair of RAID 0 would be mirrored at a higher level in RAID 1 - (is the O/S level my only choice?) - where each underlying pair is seen as a single disk. All in all, the RAID 0 offers speed due to striping, and then the RAID 1 overlays redundancy for safety.

A RAID 5 or 10 would be more desirable, in that only fewer disks are required to obtain the mutual benefits of speed and redundancy, but that would require that the SAS controller be ignored and the disks attached to the on-board SATA controller, whose difference from SAS would lose some speed, especially if the RAIDing occurred in software. Or is that speed loss inconsequential? Or would perhaps an x16 PCI-Express RAID controller be called for?

In the experience of any of you who has considered RAID options, am I thinking along the correct lines of consideration? Would you be willing to give me the benefit of your thoughts and experience?

Much obliged.

Ye Olde IT Greybeard