I use the Printables parts, they’re known good.
It’ll work, provided you have a good slicer profile and suitable printer tuned well enough that it can product parts that don’t have adhesion problems.
Ryan’s parts are carefully engineered to not need supports. The slicer can’t possibly know this, so gives warnings about parts which would otherwise have issues if not carefully designed.
The most important things for you to do in order to get good parts:
- Keep the parts in the stock configuration. Do not let the slicer flip them, and do not try to “correct” them based on your own intuition.
- Use the recommended print settings. Do not try to “improve” the prints from intuition (e.g. adding lots of walls will make things worse, not better)
- Do not use supports.
- Make sure your printer is well tuned and well calibrated before printing parts.
On that final point, lots of people print “good” parts without ever checking calibration, squareness, and other factors.
I wouldn’t start with a core, I’d start with all the small parts. I’d also strongly recommend a good set of calibration prints where you actually measure printed test parts.
Some good threads on this topic for you to read: