Can I upgrade old PC parts one by one?

Hello! I have a super old PC that is many years old and I wish to start upgrading it but I can't afford to buy the entire build at once. I will post my current state of my PC and my current plan, I wish to get some advice!
I want to use it for gaming, and I can't run multiple windows at once because my PC can't take it.

CPU
Intel Core i7 7700
RAM
16,0GB Single-Channel DDR4
GPU
Radeon RX 580

My plan - Get a Radeon RX 9070; Get another RAM to make it dual channel.

My question - What else do I need to upgrade to make sure the RX 9070 runs properly? Is it possible to buy just that and another 8GB or 16GB stick of RAM?

I appreciate the help, because I am not very tech savvy.