I'm in the middle of a few things, so here's some scattered thoughts:
I would skip the GTX 980 and jump right up to the GTX 1080. The 1080 totally blows the 980 series out of the water, Titan included. I've got a pair of GTX 980s and can run anything that isn't programmed like complete ass at a locked 60fps at 1080p, and several games (Far Cry 4, MGS5, and several others) will hold 60fps at 4K, and in some workloads a single 1080 is more powerful than that. Additionally, the GTX 1080 comes standard with 8GB of RAM while the 980 comes with 4GB.
The Titan may seem like a better deal initially since it ships with 12GB of VRAM (some may ship with 16), but you'd be giving up a lot of power for that extra 4GB (my twin 980s easily beat a Titan X...a 1080 would destroy it). 4GB of VRAM is generally fine currently, so 8GB will last you a couple of years. By the time 8GB begins to become inadequate, you're going to want to replace the card anyway.
As far as the CPU goes, a Skylake-based Core i7 is your best bet. Quad core is fine, hex is even better if it's in your budget. Thanks to both major consoles having six usable cores, developers are embracing multithreading more than ever before, so getting more cores would be good for futureproofing.
As far as SSDs go, if you can afford it I would get a fast NVMe SSD. Those are incredibly bloody fast, but the downside is the price. The next step down would be a smaller NVMe SSD (say 128GB-256GB) and use it as an OS drive, then get a Samsung 850 EVO 6Gb/s SATA SSD for your games. Next step down would be a large Samsung SATA SSD (and that's still a damn good drive, and they're getting fairly cheap nowadays).
Hope this helps! Let me know if you have any questions.