Can I find any compatible PSU with higher wattage?
I don't believe so - it's a custom form factor and I don't know that you'd be able to find anything that would fit in it. Possibly other Dell SFF power supplies, but I don't recall seeing any above 240W.
But what type of license do I need for the Optiplex 990 SFF, do I have to buy a Dell one? Or any Win 7 license will work? Also, if I buy a 32bit one, will I get the Win 10 64 bit upgrade?
I was going to suggest that of all of your options, the third is the best to me. Any version of Win7 will work, but I'd definitely recommend a 64-bit version, even if you're just sticking with Windows 7 for now. When you do the upgrade, Win7 Home will upgrade to regular Win10; Win7 Pro or Ultimate will upgrade to Win10 Pro, if that matters to you.
Also, Microsoft hasn't really put a time limit on the free Windows 10 Upgrade, and it's possible they will just make it a free upgrade indefinitely, but all we've heard so far about the free upgrade is that it would be "for a year", so if you're thinking of moving to Windows 10, I'd suggest doing it by next Spring.
Any suggestions for easy benchmarks to do on low end cards? Mostly for HTPC purposes, but I snagged a GT730, but it is the Kepler variant with GDDR5 memory.
I know some other people complained that the low end Fermi cards were better because they had 128bit memory versus 64 bit, but out of the 730s, the GDDR5 should have a fair bit more memory bandwidth than the others, and at that price point, that's usually the problem? I have a GTX750 as well, it would be nice to know the relative performance down in the basement. It's easy to find this info once you get out of the low-end.
Indeed! Those 128-bit DDR3 Fermi cards are actually significantly less capable than the GDDR5 ones. They've got 96 "cuda cores" capable of around 270GFLOPS, and 28GB/s of mem bandwidth, compared to the Kepler ones with 64-bit DDR5, which have 384 cuda cores capable of almost 700GFLOPS and 40GB/s of bandwidth. There's no real comparison.
As for benchmarks? If you're on Windows on that system, I'd suggest grabbing 3dmark. The free version has some tests which are perfectly suited to low end cards (Cloud Gate, which I used to get the numbers in the first post of this thread, and a few other scenes). You may also want to check out Unigine's benchmarks - you can run them in all sorts of resolutions and settings to test performance. They've pushed out four benchmarks now since their first one a ways back, each one more complex than the last, so they might help you gauge performance as well. The Unigine tests will also run on Linux if you're using that.