I hate to admit I only got into this after the EDA software and PCB fab services and Youtube soldering demos really hit the scene. I am a long time software engineer and it took the current ease of things to surpass my laziness barrier. I wouldn't be doing this at all if I was etching myself. Typical PCB prices are $5 per 10 two layer boards and an extra $15 per stencil. Most the price is shipping so if you order multiple projects at the same time the cost really goes down.

You make a good point about noise. If you are going to have a mixed board you better maintain separate digital and analog ground planes and perhaps even test a couple different layouts.

His pure analog schematics would be well suited to a 2 layer with one side being a ground plane and if any traces did have to be routed on the ground plane side it would be easy enough to ensure they were out of the way of any return paths.