Sorry for the delay, my router crashed.......
I dont live in the UK, so i cant tell you where to buy it, but i checked all parts and they should be compatible
Here's a link to a website that i use a lot when building or modifying computers, might help you out
https://pcpartpicker.com/
Also i found a YouTube video so you can check the performance of the GeForce GTX 1050ti(it's called ti because of the 2 extra gigabytes of ram. You get a lot more if you get the ti version instead of the stock one.)
https://www.youtube.com/watch?v=58gic2yCS3A
There is a lot of different brands who make the GTX 1050ti, i would recommend you get the EVGA version, because it only has 1 fan, and the case is pretty small, so i don't know if the other version will fit into the case.
Here's a link to the EVGA card, you shouldn't buy the card from their official site, but it gives you an estimated price for the card, and an overview of what you can expect from the card.