hi im new to building gaming computers

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Don't really need the 850 Pro. Can easier get a decent 256GB SSD at that price point.

That MSI GTX 1070 is overpriced, you can get a 1070 FE or even a custom 1070 for £400-420.
https://www.overclockers.co.uk/pc-components/graphics-cards/nvidia/geforce-gtx-1070?sPage=1&sSort=3

Don't really need a 750W psu if you only plan to run a single graphic card.

The motherboard only has one usb 2.0 header. If you require more usb 2.0 headers, you may be interested in using adpadter or usb 2.0 expansion card:
https://www.amazon.co.uk/Motherboard-20Pin-Header-Female-Cable-Black/dp/B00H8V2DD6
https://www.amazon.co.uk/NZXT-IU01-ACC-NT-IU01-R-Internal-Expansion/dp/B0031ESKJA
Don't really need the 850 Pro. Can easier get a decent 256GB SSD at that price point.

That MSI GTX 1070 is overpriced, you can get a 1070 FE or even a custom 1070 for £400-420.
https://www.overclockers.co.uk/pc-components/graphics-cards/nvidia/geforce-gtx-1070?sPage=1&sSort=3

Don't really need a 750W psu if you only plan to run a single graphic card.

The motherboard only has one usb 2.0 header. If you require more usb 2.0 headers, you may be interested in using adpadter or usb 2.0 expansion card:
https://www.amazon.co.uk/Motherboard-20Pin-Header-Female-Cable-Black/dp/B00H8V2DD6
https://www.amazon.co.uk/NZXT-IU01-ACC-NT-IU01-R-Internal-Expansion/dp/B0031ESKJA
 
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