Graphics - I currently have a GTX 1080 in my computer, which seems fine. I just thought I may as well upgrade while I can and hopefully it will last me a long time. It's the first time I'll have built a computer and I don't plan on doing it again anytime soon.
PSU - that sounds good, its a shame there isn't a 650w that I can have in the RMx. I know they do on Amazon but on pcspecialist site they start from 750w.
What AMD would you suggest above the i5? Although it doesn't seem that I can change that now, only Intel's are listing in my order.
I would honestly drop the GPU in that case and use your current one. You're getting no meaningful upgrade from the 1080 to the 2060. They are both high end 1080p gaming cards, getting on for 1440p also.
This would save you a significant wedge of cash for no performance hit.
If you have Windows 10 you can transfer the license also. You can get a very high end rig for a very good price if you spend wisely
You would need to cancel your order and re-create a new order. What is your budget?