I’m in the process of doing something similar and found this site https://pcpartpicker.com
You can pick and change your parts, read reviews, check compatibility etc and most importantly (to me anyway) ensure you don’t miss anything. It’ll then tell you where the parts are available and at what cost.
Be sure to change your country in the top right.
You can save your setup, here’s what I’m thinking about getting: https://uk.pcpartpicker.com/list/NBcXgL Once I realised that coloured components are no more expensive I decided to try a white themed setup as it’ll match the office better. I’m going for a SU/Lumion setup so my requirements are different to yours.