I might suggest you buy a I3-7350K bundle with a z270 motherboard and a 2 x 4gb kit of ddr4 ram for £344.99
https://www.amazon.co.uk/dp/B06X9MQ5GP/ref=sr_1_2?ie=UTF8&qid=1500590801&sr=8-2&keywords=i3-7350k+bundle
The I3-7350K was initially overpriced but that price has dropped.'
It runs at 4.2 but it can be overclocked to around 5.0.
Considering that the prices of RX-5xx cards and similar are very overpriced due to mining, I suggest you initially build using the excellent integrated HD630 graphics and see how you do.
A top quality Seasonic S12II 620w psu should be around £60.
It will support a future discrete graphics card as good as a GTX1080ti.
Cases are a personal thing, so most will do. Bust your budget if you need to for a case you love. It will be with you for a very long time.
I suggest buying a Samsung evo 240gb ssd for your C drive. about £100.
Defer on the hard drive until you actually need bulk storage space.