First: Get a 3d printer, if you don't have one. No quicker way to turn ideas into physical objects for prototyping and iteration.

Second: Pick a project with modest but not trivial goal. Something that exists within the state of the art on at least most axes. e.g. make a quadcopter, make a 3d printer, or make an automated cat food dispenser. The project can be special on an axis, e.g. I want the break the drone speed record, or make the best battle bot for a weight class - but stacking too many novelties into a project compounds the difficulty.

Three: Break down the project into manageable sub tasks, starting simple then working towards integration. E.g. step 1, make a drone motor spin. Step 2, make a drone motor spin at exactly 2503rpm. Step 3, design a housing to fit four drone motors/control board/battery, etc. It's perfectly natural/common/fun to play this by ear, many projects will go back and forth between biting off more than you can chew and isolating model systems for testing.

Four: Integrate the subsystems, test, debug and most importantly repeat.

[0] The Bambu a1 mini is a perfectly competent entry-level product. And Fusion360 is a solid CAD for design side.