I have fallen into the JLC trap. The boards are effectively free, you just pay for expedited shipping. That gets 2 layer boards here in about a week, 4 layer in about 10 days. I have also used a range of the other PCB houses in Asia, to varying levels of success.
Another EU based supplier is Ragworm
And I always recommend comparison shopping on a site like PCBshopper
A daunting task in the best of times. The real answer is most people go with what they know. So as you’re building that out, you’ll have to figure out what works. I think pilfering from other schematics you find of devices you’re using also helps, though that usually leans more towards simple OSHW type designs. After that, I like going to app notes before I go into datasheets. And for power stuff, I’m a bit of a convert to tools like WebBench and other tools.
This was a big swap for me, I used to think this was “cheating”. But now I know it’s just a best practice and it’s usually the first thing I seek out. It has saved me many times now.