Like you, I find the hardest thing to do well in a project is the physical assembly.
I've learnt a few things. First, use off the shelf products where available rather than 3d print something that will always be an inferior imitation.
Use 3d printing for an object you can't get off the shelf.
3d printing excels in detail. The printer doesn't care how intricate the object is. Go wild with detail.
You can make a neat round hole in a PLA object with a soldering iron. PLA takes spray painting well.
To me, large objects are not worth the extreme print times.
John.