OK, will try to be succinct, but there is a lot to cover.
I used the machine specs you forwarded as the basis for the build you should aim, I say basis because the box you forward is neither a gaming box or a professional station.
To start you need a decent case, something quality built that will last and will accommodate any future update and fairly sound isolating.
Go for a:
Phantek - Eclipse p400S ATX mid tower. 80$
The 350W power supply on your base model is tight. You can go for a 500W model, but if it is to last and again accommodates future upgrade you should go for:
Power supply: Corsair builder CXM 750W Modular 80 plus bronze PSU 69.99$
The motherboard suggest is over the top for what you need, I suggest the one below whic is almost 75$ for the same delivery of goods.
Motherboard: Gigabyte LGA1151 Intel Z170 ATX DDR4 Motherboards GA-Z170-HD3P 145$
Storage (hard drive). Here you want to go for pure speed to precisely reduce that annoying loading issue you mention. In this case go for a solid state more specifically a M.2. Go for 256GB, you dont need more for a trading station.
Samsung 960 EVO Series - 250GB PCIe NVMe - M.2 Internal SSD (MZ-V6E250BW) 128$
Memory, do yourself a favour go for 16 GB its just ridiculous to go for less. The DDR4 are slightly more expensive, you can go for a DDR3 that deliver similar speeds but drink more, so spend more electricity, even if its cheaper when you buy.
2x8GB Patriot Viper 4 DDR4-3400MHz 145$
Now the CPU. You dont need a Core I7, but I understand that you want it to last for along time. If you want to save money go for a Core I5
Intel Core i7-7700 Desktop Processor 8M Cache, 3.6GHz (Max Turbo Frequency 4.20GHz) 7th Generation 299.98$ (the one on your link)
Intel Core i5 6500 3.20 GHz Quad Core Skylake Desktop Processor, Socket LGA 1151, 6MB Cache BX80662I56500 195$
Regarding the cooling for the CPU, you absolutely do NOT need water cooling. You are not overclocking anything or doing any mooding.
You could use the cooler that comes by default with the intel CPU. Sill if you want to be extra careful and cover future upgrades you go for:
Be quiet! BK002 Shadow Rock CPU cooler 48$ Its big! But it delivers, set it to lower rotation it will deliver with utmost silence. You will appreciate a silent machine running when you will stand next to one. You will realise that vanilla PC are so noisy.
Lastly the graphics card. The one on the link is a mid range gaming card. It will support your monitors for sure but its not designed for this purpose.
Still if you want to spend equivalent money for equivalent power you should go for:
PNY NVIDIA Quadro K1200 - ( VCQK1200DP-PB) 310$
The graphics card above is very good, the card will support 4 monitors with 4k resolution. No offence but i reckon yours are not. Mind what type of connectors your monitors support! Adapters might be needed.
So you can go for much cheaper for plain monitors.
PNY NVIDIA Quadro P600 Professional Graphics Board - VCQP600-PB) for 160$(?)
I added to you are likely to spend more money than this. In things that do not come to mind. Like cabling, adaptors, arms for the monitors or otherwise bigger desk.
I hope i have not forgot anything, it was a busy day. Feel free to ask anything, as you can imagine i skipped alot of technical stuff.
All the best,
P.S,- If attaching a external drive, for god sake use the 3.1 USB port! USB ports are not all born alike.