Thank you very much, will probs try this for the short termI would personally go for a 1TB Crucial MX500 SATA SSD for around £100
That will offer good performance at the moment for gaming, then once you've got your new build you can just swap it into that into a spare SATA slot as a game drive or even storage.
They're rediculously easy to install, literally plug in a SATA Data and seperate power connector, and done.
Then to install windows, you can create a bootable USB from here (assuming you're on windows 10):
If you need any help, just post here and we can guide you on getting setup.