Some of the steps along the way of building my Prusa RepRap. I printed all the parts at Fab Lab Tulsa (mostly on a Thing-O-Matic), pretty much one at a time. I sourced pretty much every part myself (Cutting rods, rethreading rod ends, buying individual nuts etc. I would highly recommend NOT doing that for your first build). I even wired up my electronics on a blank arduino Mega shield (once again I would NOT recommend doing that for your first build, buy a RAMPS or something). It printed with my electronics until I changed firmwares and the stepper pulses became too quick for the opto-coupled stepper drivers I was using. I ended up building a Ramps (in kit form) and it works perfectly.
If you can print your own, or have someone with a 3d printer print your printed parts.
Buy a set of threaded and smooth rods (pre cut for your printer version).
Buy a hardware set (nuts, washers, pulleys etc)
Use an established (like already set up in firmware versions) printer controller (like Ramps 1.4)
Don’t be too worried about SAE vs Metric. Once your frame is together it will probably stay that way (just be consistent (ie. you probably won’t have to get anything that is not in your hardware kit)).
I personally found Marlin to be an easier firmware to use than what I started with (still some configuration required obviously).