The motherboard instruction manual should give you a step by step walkthrough of installing. But yeah, for the most part. It's literally impossible to put things in the wrong slot in the wrong orientation. You should do what my dad did with the first computer he bought me. He got the parts, and made me put it together as a "learning experience". Just keep in mind cable management for the power, so as to not obstruct airflow, and also proper fan orientation.

You want the biggest, strongest fans blowing OUT. The reason is Bernoulli's principle: PV=nrT, where P = pressure, V = Volume, n = number of moles, r is a constant, and T = temperature. So, if you have the largest fans blowing out, that drops the pressure, temperature has no choice but to go down. Aside from this, and cable management, the manual should draw attention to things you need to know. Also, remember to budget for the operating system.

I'd check through this. You should be careful though since PS4s are often times sold at a lost or were sold at a lost in the past.

If you go cheaper than say $500 it might not be much of an upgrade at all really. IDK for sure myself.

9 is probably the best way to go unless you go for a 1660 / 1660 TI card and go to the $700-$800 price range.

https://www.techsiting.com/cheap-pcs-for-fortnite/