LOLitsNCIX

Almost everyone uses night theme (even Linus IIRC) so why isn't it the default?

Unkindness, if you could tell us why you are building your computer, we might be able to help you out more. It sounds like you are going to game, but we aren't sure. Also, these deals aren't really that good, with or without tax. I'm also not sure why you are trying to use a GTX 1050 with an i9, not even a 1050Ti. I personally would recommend to just get a 1070Ti, 1080, or 1080Ti and just skip RTX overall. RTX is not going to have a price drop for a long time, and RTX is only marginally better than the 1000 series. 
 
TL;DR Ditch the i9 and RTX. Get an i5 or i7 (Or Ryzen 5 or 7), which gives you the option of a cheaper motherboard, and a 1070-1080Ti (any of those 4 cards), or an AMD equivalent.

Even if you are going to be using this computer for "just about everything a computer can be used for", I have a computer that does all of this and only has a low-end i5. I can send you the specs if you'd like. An i9 is seriously overpowered for this work, especially being paired with only a GTX 1050 as you suggested. Don't get an RTX card in the future, but instead just get a GTX card now. The 1000 series is more than enough for anything you would need today and is going to be plenty in the future as well. 
 
My Recommended Parts List:
i9 9900k (since you are so set on it)
16GB DDR4
GTX 1080 (Or AMD Equivalent)
And a PSU, Motherboard, Case, Fans, and storage of your choice

PCPartPicker part list / Price breakdown by merchant
CPU: Intel - Core i9-9900K 3.6GHz 8-Core Processor  ($579.99 @ B&H)
CPU Cooler: Noctua - NH-D15 82.5 CFM CPU Cooler  ($84.35 @ Newegg)
Case: Fractal Design - Meshify C TG ATX Mid Tower Case  ($89.49 @ Newegg)
Power Supply: SeaSonic - FOCUS Plus Platinum 650W 80+ Platinum Certified Fully-Modular ATX Power Supply  ($89.99 @ Newegg)
Case Fan: Noctua - NF-P12 redux-1700 PWM 70.8 CFM  120mm Fan  ($13.90 @ Amazon)
Case Fan: Noctua - NF-P12 redux-1700 PWM 70.8 CFM  120mm Fan  ($13.90 @ Amazon)
Case Fan: Noctua - NF-P12 redux-1700 PWM 70.8 CFM  120mm Fan  ($13.90 @ Amazon)
Total: $885.52
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2018-10-31 10:08 EDT-0400
 
Even assuming the 3x Noctua NF-P12s are included in your $850 price, that still isn't that great of a deal, certainly not to the point that you would be needing be hush hush about it acting like it has fallen off the back of a truck. Do your prices include tax or do you still have to pay tax on top of that $850?
You could get the full Ryzen 2600 + RX 580 system I suggested earlier for $850 which will be perfectly fine for gaming at 1080p.

Unkindness, if you could tell us why you are building your computer, we might be able to help you out more. It sounds like you are going to game, but we aren't sure. Also, these deals aren't really that good, with or without tax. I'm also not sure why you are trying to use a GTX 1050 with an i9, not even a 1050Ti. I personally would recommend to just get a 1070Ti, 1080, or 1080Ti and just skip RTX overall. RTX is not going to have a price drop for a long time, and RTX is only marginally better than the 1000 series. 
 
TL;DR Ditch the i9 and RTX. Get an i5 or i7 (Or Ryzen 5 or 7), which gives you the option of a cheaper motherboard, and a 1070-1080Ti (any of those 4 cards), or an AMD equivalent.