Hi all!

I read many reviews on this website and I found them very useful.
I already have a general idea, but I still have some doubts. I waited for the 8th gen i7 to be released and now I am ready to build a new gaming computer. I will use it for gaming and for some work where multithreading is very useful (astrophotography processing).

So far here is what I considered:
- Fractal Design Arc Midi R2
- Intel i7-8700K
- Cooler NZXT Kraken X52 Rev. 2
- ASUS Maximus X Hero or MSI Gaming M5 or MSI Pro Carbon AC
- DDR4-3200 2x8GB
- MSI GeForce GTX 1080 Ti Gaming X
- Corsair AX860i PSU
- Samsung 960 EVO 512GB M.2 + Seagate FireCuda 2TB
- BR/DVD reader/writer (I will likely pick a DVD writer, I'm not planning to watch movies on the PC)
- Corsair mouse and keyboard
- Monitor 1440p 24", in the future I will use 2 monitors

I'm not planning to pass the 3000$ mark and this configuration is within this limit so far.
I highlighted in bold what I haven't decided yet.

Motherboard
My understanding is that, really, at the level of the boards indicated the performance is pretty much the same.
I think that the Gaming M5 is a very nice board, that comes with a set of accessories and features. I don't plan to perform hardcore overclocking, but I'm planning to boost the frequency in the future, so I don't need an extreme OC board but a reasonably featured one.
Any recommendations with reference to this?

RAM
I don't think that spending a lot of money for higher frequency memory automatically grants higher performance (in real life I mean, not in benchmarks).
Considering the price of DDR4, I think that right now buying 2x8GB is enough, with the option of buying 2 more 8GB banks in the future.
I am considering the G.Skill and the Corsair Vegeance.

Storage
Initially I was considering a single 1TB M.2 Samsung 960 Pro, but for the price of a 1TB M.2 drive I can get a 512GB one + 2TB hybrid drive + about 130$ left.

Monitor
The idea here is to avoid spending too much, but still get a valid screen with 1440p resolution.
I would like to buy a 24" screen with the option of adding a second screen in the future.
A friend is selling a Lenovo L24q, but my understanding is that for the money I can find much better screens on the market.
Any suggestions? What other models should I consider?

Thank you for your comments/suggestions!