Upgrade Overkill , what can go?

Current Machine:
CPU: Intel - Core i5-3570K 3.4GHz Quad-Core Processor 
Motherboard: ASRock - Z77 Extreme4 ATX LGA1155 Motherboard 
Memory: G.Skill - Ripjaws Series 8GB (2 x 4GB) DDR3-1600 Memory 
Storage: Samsung - 840 Pro Series 128GB 2.5" Solid State Drive 
Storage: Seagate - Barracuda 500GB 3.5" 7200RPM Internal Hard Drive 
Video Card: MSI - GeForce GTX 780 Ti 3GB TWIN FROZR Video Card 
Case: Fractal Design - Define C ATX Mid Tower Case  
Power Supply: EVGA - SuperNOVA G3 650W 80+ Gold Certified Fully-Modular ATX Power Supply  
Operating System: Microsoft - Windows 10 Pro Full 32/64-bit  
Monitor: LG - 24GM77 24.0" 1920x1080 60 hz
Mouse: Razer - DeathAdder Wired Laser Mouse 
Headphones: SteelSeries - Siberia 350 (Black/Orange) 7.1 Channel  Headset  



1. What is your budget? £1000 (UK based)

[font=Open Sans, Arial, Helvetica, sans-serif]2. What will be the main purpose of the computer? Gaming (Witcher 3, Overwatch), Multitasking (screen real estate a must) programming (R & Phyton), Scientific analysis, bioinformatics (Next generation Sequencing, etc) [/font]Linux Dual boot might be on the cards

3. Do you need a copy of Windows? No

4. Can you use any parts from an old computer? GPU, storage, case, PSU, Mouse, headset, Keyboard

5. Do you need a monitor? Yes, I use a 5K 27 inch IPS in work (2017 MAC) and I just can't stand the sight of my 24 in TN panel at home. 

6. Do you need any of the peripherals? I'd like a nice keyboard with low noise typing that would be ok for gaming.

7. Are you willing to try overclocking? Yes unless a non K version processor offers a lot of saving.

8. How can you pay? Cash, card, BT
[font=Open Sans, Arial, Helvetica, sans-serif]9. [/font]When am I buying? [font=Open Sans, Arial, Helvetica, sans-serif]This summer, Probably get monitor first and follow up in June for everything else. Happy to wait for hardware refreshes.[/font]

The Case and PSU are new, the monitor is god awful. I need more storage space if I get into the type of analysis I'm thinking of doing, I need a lot of RAM, but it's so expensive that I think I would just get 16 GB and upgrade to 64 later, although slots might be an issue. 

[font=Open Sans, Arial, Helvetica, sans-serif]Ideal new Build[/font]
[font=Open Sans, Arial, Helvetica, sans-serif]CPU: Intel - Core i7-8700K 3.7GHz 6-Core Processor  (£281.94 @ Aria PC) [/font]
[font=Open Sans, Arial, Helvetica, sans-serif]CPU Cooler: CRYORIG - H7 49.0 CFM CPU Cooler  (£34.99 @ Overclockers.co.uk) [/font]
[font=Open Sans, Arial, Helvetica, sans-serif]Motherboard: ASRock - Z370 Extreme4 ATX LGA1151 Motherboard  (£138.91 @ Amazon UK) [/font]
[font=Open Sans, Arial, Helvetica, sans-serif]Memory: G.Skill - Trident Z RGB 16GB (2 x 8GB) DDR4-3000 Memory  (£190.06 @ Amazon UK) [/font]
[font=Open Sans, Arial, Helvetica, sans-serif]Storage: Samsung - 960 EVO 500GB M.2-2280 Solid State Drive  (£192.50 @ Aria PC) [/font]
Subtotal £838.4

New Monitor
[font=Open Sans, Arial, Helvetica, sans-serif]Monitor: Asus - ROG Strix XG35VQ 35.0" 3440x1440 100Hz Monitor  (£784.98 @ Ebuyer) [/font]

Total: £1623.38

Questions
1. The monitor is overkill. I do want real estate for multitasking but perhaps I do not need this, a 16:9 27 inch would do me just fine. IPS/VA only. Don't really know much about high refresh rates so part of me wants to get a second hand 27in 1440p/4k 60 hz with low latency. I'm worried about 2K being noticable **** compared to the gorgeous 5K display in work. Completely out of my depth on this.

2. I was shocked by RAM prices, Some of the stuff I will be doing requires 32-64 GB ram. Could I get a single stick of 16G RAM, and get another stick later, or would the single channel RAM be a bad idea, I've no idea what ram speed actually does so I just picked the 3000 (units?) version?
3. I have a 780 TI, I'm happy with this due to prices atm and I try and game at 2K, lol.
4. Where can I compromise to get this down to £1000?
 
Cheers guys!