Leave the final art until later. The reason is that you probably don't know exactly what art you need at the beginning. If you buy or create art before prototyping the game, you are likely to find that some of it doesn't meet your needs and has to be redone or replaced. It's generally best to start with placeholder art and fill in the real art as you go. A five-second scribble or grey box works just fine at an early stage.
As for how to get started, if you don't have a programming background, I would probably just pick a free engine like Unity or Godot and start doing the tutorials. They start out very basic. What technologies work best for a given project just depends on the nature of the project and your personal preferences. I would really recommend doing some small projects first to get used to the process, decide if you like the tools you are using, and get some rookie mistakes out of the way. If you are starting from scratch and try to jump straight into a large and complex project, you will probably have a difficult time.