1) Are there any compatibility issues with the selected components?
Motherboard are not yet supported unless you upgrade it's bios by using skylake cpu. Its a risk, don't do it. And you don't need the TP-link network adapter, its already has one build in the motherboard. Same for sound card, use the onboard first, if its not good enough, you can upgrade it anytime.
2) Can I save some money from certain parts while keeping the same performance?
I will try give better build later
3) What kind of UPS should I buy to protect the system?
UPS is not mainly to protect the system. Stabilizer did. UPS is more like power buck up, but reputable brand has stabilizer build in. Then again reputable brand is expensive
4) I am planning on buying the parts from Europe since I live there. Will it be cheaper to order them from the US? (I doubt)
US is a heaven for pc part. I live in Asia and envied all the time the US price tags. When they are on promotion, the price is unbelievable cheap
5) Will prices fall over the next 5 months?
It always does. Ryzen AMD has arrive, it should move the price.
1) I selected the Intel core i7-7700K because I found that the price gap between the i7-6700 or the i7-7700 was not that big
Yeah but the motherboard you chose cannot even do overclock, so its just wasting money. i7-7700 came with standard heatsink while i7-7700K doesn't, it should save at least $10 (yeah i know its not great heatsink, but it will do its basic job done)
2) I don't care a single bit about colors and stuff like that
same here
3) I did not choose an external hard drive or a mouse because I already have one
internal hard drive is recommended as the SSD still more expensive for storage. But its fine if you already have external HDD
4) I am planning on building this computer over the summer, and my budget will be around 1400€ (or 1491.77$)
Here is my first suggestion:
PCPartPicker part list /
Price breakdown by merchant
CPU: Intel Core i7-7700 3.6GHz Quad-Core Processor ($295.49 @ SuperBiiz)
Motherboard: ASRock B250M-HDV Micro ATX LGA1151 Motherboard ($66.98 @ Newegg)
Memory: G.Skill Ripjaws V Series 16GB (2 x 8GB) DDR4-2666 Memory ($99.97 @ Jet)
Storage: Samsung 960 Evo 250GB M.2-2280 Solid State Drive ($129.99 @ B&H)
Video Card: Gigabyte GeForce GTX 1070 8GB Windforce OC Video Card ($379.00 @ Jet)
Case: BitFenix Comrade ATX Mid Tower Case ($27.99 @ NCIX US)
Power Supply: SeaSonic S12II 620W 80+ Bronze Certified ATX Power Supply ($49.90 @ B&H)
Optical Drive: Asus DRW-24B1ST/BLK/B/AS DVD/CD Writer ($18.88 @ OutletPC)
Operating System: Microsoft Windows 10 Home OEM 64-bit ($92.99 @ B&H)
Monitor: Acer G257HU smidpx 25.0" 2560x1440 60Hz Monitor ($254.99 @ Jet)
Keyboard: Redragon Karura K502 Wired Gaming Keyboard ($33.26 @ Amazon)
Total: $1449.44
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2017-03-13 21:45 EDT-0400
Ok, for my 1st suggstion its an i7 with GTX 1070 and samsung 960 evo. The 960 evo has more than 2x the speed of standard SSD, its worth it when you can afford it. It will safe your time a lot in loading and writing data. Your life is more precious than money , don't you agree?. This build should not need any upgrade until the end of GTX 1070 and should be able to cope with new gpu you can throw in the future as long as 620W psu can manage it.
Next is the 2nd choice. Its uses the new but cheapest AMD ryzen 1700. What makes it interesting is that i7 has 4 core 8 thread when this ryzen has 8 core 16 thread. Well, its the latest cpu from AMD after the long wait. For your information, more and more game will adapt using more thread. That is why "i5 killer" game was created recently since i5 only has 4 thread. i7 still a safe bet, but why not take a risk with something almost double the thread with only few dollar difference.
Here are 2nd choice:
PCPartPicker part list /
Price breakdown by merchant
CPU: AMD RYZEN 7 1700 3.0GHz 8-Core Processor ($328.89 @ OutletPC)
Motherboard: Asus PRIME B350M-A Micro ATX AM4 Motherboard ($89.99 @ B&H)
Memory: G.Skill Ripjaws V Series 16GB (2 x 8GB) DDR4-2666 Memory ($99.97 @ Jet)
Storage: Samsung 960 Evo 250GB M.2-2280 Solid State Drive ($129.99 @ B&H)
Video Card: Gigabyte GeForce GTX 1070 8GB Windforce OC Video Card ($379.00 @ Jet)
Case: BitFenix Comrade ATX Mid Tower Case ($27.99 @ NCIX US)
Power Supply: SeaSonic S12II 620W 80+ Bronze Certified ATX Power Supply ($49.90 @ B&H)
Optical Drive: Asus DRW-24B1ST/BLK/B/AS DVD/CD Writer ($18.88 @ OutletPC)
Operating System: Microsoft Windows 10 Home OEM 64-bit ($92.99 @ B&H)
Monitor: Acer G257HU smidpx 25.0" 2560x1440 60Hz Monitor ($254.99 @ Jet)
Keyboard: Redragon Karura K502 Wired Gaming Keyboard ($33.26 @ Amazon)
Total: $1505.85
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2017-03-13 22:10 EDT-0400
You can look the rough comparison between i7 and ryzen 1700 in below link
http://cpu.userbenchmark.com/Compare/Intel-Core-i7-7700-vs-AMD-Ryzen-7-1700/3887vs3917
Its up to you
Good luck