New PC Build - Questions/Advice

[Bardalicious]

So I started building a new desktop PC last week.. this is the first time I've built my own in probably 8 years or so since my last purchase was a gaming laptop for portability.

So far my components are:

CM Storm Stryker - White Full Tower Gaming Computer Case with Handle and External 2.5" Drive Dock

EVGA SuperNOVA 1000 G3, 80+ Gold 1000Watt fully modular PSU

MSI Z270 XPOWER GAMING TITANIUM LGA 1151 Intel Z270 MoBo

Intel Core i7-7700K Unlocked Kaby Lake Quad-Core 4.2 GHz CPU

G.SKILL Ripjaws V Series 32GB (2 x 16GB) 288-Pin DDR4 SDRAM DDR4 3200MHZ

SAMSUNG 960 EVO M.2 250GB NVMe PCI-Express 3.0 x4 Internal Solid State Drive

I'm using the M.2 NVMe SSD just for windows and important system software like malwarebytes and kaspersky, which leaves me enough room left over for installing any games I need the most performance from. I've got a standard 7200RPM SATA HDD for storage as well from my last desktop but I'll be replacing it with a SATA SSD, or perhaps an M.2 SATA just for tidyness in the case to limit cable usage. And eventually I'll probably add in another set of the same 32gb RAM and look into liquid cooling as well, since the MoBo I bought is very OC-friendly.

Now, I currently have an old graphics card in this tower (gtx 260, yuck), just so that I could get everything set up to ensure that none of my parts came DOA, and to get windows installed, drivers updated etc.

I'm looking for feedback on GPUs now, if anyone has built a new PC recently or upgraded their video card at least. I know I'll be going with NVIDIA for sure. I'm sort of leaning between the GTX 1080ti and of course the good old TITAN X.

Then comes the question of using dual GPUs in SLI or sticking with the one. I haven't found a definitive answer on that one. As I understand it, on most motherboards you've got a limited number of PCIe data channels.. 20 total? 16 for the first PCIe slot for the graphics card to use, then 4 more dedicated to the motherboard which my M.2 NVMe SSD is using. Adding a second GPU drops both cards down to 8 a piece, though I don't know if that makes a huge difference with the increased processing power. Then of course not all games even recognize SLI cards so..

Any advice on what card I should go with, whether to use SLI or not, etc or even critiquing my build would be appreciated. Advice on whether i should go with another M.2 NVMe SSD for storage or an M.2 SATA SSD or a standard SATA SSD would be helpful as well, i dont fully grasp the whole PCIe lanes thing yet, so i dont know if adding a SATA SDD instead of another NVMe would have any advantage or not. Note that this is simply a gaming PC, I'm not using it for deep learning, cryptocurrency mining or the like.

(Yes I know this isn't Toms hardware or overclockers forums but I do know there are other PC enthusiasts here!)