1. Slightly cheaper MSI motherboard. If you prefer Gigabyte, you can add it back, it's only a difference of a few dollars.
2. I found you faster RAM for 2 cents more. Also, 2x4GB dual channel is recommended over 1x8GB single channel for slightly better performance (up to ~10%). You shouldn't really need to worry about running out of RAM slots.
3. The newer Crucial BX100 is $20 cheaper than the MX100 for nearly the same amount of storage. You won't be able to tell the difference in SSD performance when it's measured in seconds.
4. The biggest change - if you're on a tight budget, I recommend the R9 290. Costs a lot less, but it's in the same neighborhood when it comes to performance. Should handle 1080p gaming on high settings for the next few years.
5. Cannot really recommend Corsair CX power supplies, they're the "budget" line made with cheaper components. For $8 more, you can get a much higher quality EVGA Supernova B2 750 watt model which has more capacity, semi-modular cabling, and is made by Super Flower, one of the respected power supply manufacturers. It got a great review by Jonny Guru.
6. Dropped the DVD drive as it's not really needed nowadays. USB drives and digital distribution have removed all need for it, and Windows can be officially installed via USB drive (it's actually faster) with the help of a Microsoft tool.
7. The $30 Gigabyte wifi adaptor is better. It has more features and support like bluetooth and Wireless AC, as well as the fact that the antenna is on a wire you can place yourself for better reception, instead of having short antennas sticking out of the back of the case.
Thank you! This is extremely helpful, especially the RAM, SSD, and wi fi recommendations. My knowledge is pretty limited at this point, so it's great to get feedback.
I like the idea of future-proofing as much as my budget will allow, but if you don't think I'm sacrificing much, I will go with the cheaper motherboard and graphics card. I suspect that even if I went with the GTX 970, I'd still be tempted to upgrade the same number of years down the line.
As for keyboards, I probably will just go the bargain route you recommended. Mechanical keyboards sound like a lot of fun though, so maybe I'd plunge for one of those if there's a good sale.