They haven't produced any 1366 socket CPU's since 2012. What I'm referencing is buying a used Xeon off of Ebay. The X5650 is the cheapest of the X56xx series of Xeon CPU's that you can get for your system. They overclock extremely well and run a lot cooler than the 45nm CPU's (i7 920, 930, 940, 950 960). For 20$ you get a CPU with 2 more cores, 4 more threads, more cache, higher stock QPI frequency, better temps, better IPC, and higher OC potential.
USB 3.0 is whatever, you could just as easily get a PCIe card for USB 3.0 ports.
Those memory sticks are probably dual rank when taking their age into consideration but so are pretty much any 3x2GB kits you would find on ebay and yes, they'll all work together. The ones you have though have extremely tight timings so if you plan on using XMP and don't have sticks that can match those timings at 1600mhz then you'll have to manually adjust the timings to something the slowest memory in your system can run at. It might just be easier to pick up 3x4gb sticks like the ones I linked to and sell yours. Will put less strain on the IMC using 3 sticks instead of 6, both ways get you to 12GB.
Aside from that... You'll still want a better graphics card than a 285 to use for today. I have one in storage at this point, can't really think of a use for it but I put a massive aftermarket cooler on it so I'm keeping it around.