A:Answer 1) Most of their components are picked from whatever is available in their stock at the time of building, including the motherboard and graphics card. The only thing guaranteed is the processor (Intel 8700k), 32 GB ram (any brand), 250 GB SSD (any brand), 3 TB HD (any brand), GTX 1080 TI 11GB video card (any brand).
2) Would imagine the system can run with a GTX Titan V... but why would you, when that single graphics card ITSELF costs more than this entire system (including the GTX 1080 TI) does.
3) The case this comes with does not appear to have front slots to allow addition of DVD/DVDRW/Blueray drives, etc, even though the interior has more than enough room for you to add them in.