For me, designing for yourself in CAD is always going to be favourite but then it’s sort of my job and I’ve been doing it for decades.
Not sure how viable modern 3D scanning for print production is; I suspect it must be pretty good these days. But I imagine you may still want to tinker with the model, so you’re back to some sort of CAD again.
There are probably plenty of folk on here that would be more than happy to do the CAD side for you, given suitable instructions to work from.
Finally, while the ability to pretty much design and print anything you might need, there are inherent limitations to 3D printed parts, mostly in terms of strength, due to materials and construction method. I’ve had a couple of “spare part” projects fail because although the parts were a perfect fit, they weren’t man enough for the task.
I should note that I’ve only used TPU and PLA, so there may be other options that fare better, but I have no desire to start using carbon fibre infused filaments, etc..
On the other hand, I’ve also had some great successes. You just have to pick your battles.
PS: Take a look at this thread. There may be one or two others on the topic as well.