I am really struggling to wrap my head around what we need and getting overwhelmed with all the different things to keep in mind (and how features interact)
We don't have a huge budget (~£500, possibly more 
?), but don't mind a reconditioned machine, nor are any of us serious gamers (yet anyway). But we would like to be able to play games like Minecraft, Sims 4, Eastshade and Witcher. It also needs to function well enough as a homework computer for DC.
My main points of confusion are all the different graphics cards, and what sort of processor we need alongside. I know various parts can be upgraded in time, but are some machines easier to do this with than others?
If anyone can help point me to any sites that explain the basics really well, or if anyone can explain any important things to note/mistakes not to make etc, I would be so grateful!