MoonMan2,
1) Yes, it will work. The motherboard is designed for quad-channel memory configuration, however when you install 2 sticks in slot's A1/C1, it will work just fine for dual channel.
2) Generally, the on-board sound is quite good. In truth, it really depends on your sense of hearing. To some, the on-board sound's like a nightmare, to other's it's pleasant. If you decide to connect speakers for a 6 or 8 channel configuration, the sound output relies on the clarity of your speaker's. If you decide to buy Logitech or other manufacturer's, you won't regret the expense 🙂
3) There's so many SSD manufacturer's out there nowadays, that it frankly doesn't matter which one you choose. Generally, the read/write speed's won't differ to much. You will find a couple SSD's with a bit faster sequence's but honestly, I doubt you will see the difference. I have Crucial's model, MX500 1TB, for a total of four. I can't complain about anything. Which model's are you intended on buying? Conventional SSD, M.2 or PCIE 3.0 x4? The last two option's are dissimilar because the read/write speed's are much faster.
4) Well, to be honest, from reading your post, I discovered that my motherboard has the same definition for the USB 3.1 ports. I'm not sure what exactly it mean's, however I have my mouse, keyboard and Razer pad connected and it all work's fine 🙂