Most of it's common sense, to a point.
1) you get all your bits, lay it out on a surface bearing in mind things like EMF interference with high gain parts of a circuit, heat etc. I usually do a rough sketch on scrap paper.
2) Don't mount electrolytics next to big dropping resistors, we've all seen this done on commercial PCB's
3) In my case mounting stuff is dictated by what I have and/or can make.*
4) a good pair of calipers, scraps of paper and the jobs a good un.*
5) If you go on DIYaudio and search on this there are loads of threads on the subject, but mostly fettling metal etc is down to experience and getting your hands mucky, you learn by doing and making mistakes.
6) & 7) & * ... there are pro enclosure, panel fabricators here in the UK and in the EU that has relatively easy to use software, see -
https://www.metcase.co.uk/en &
https://www.quickpanel.sk/en/gallery...e-front-panels as well as
https://www.penn-elcom.com/
Hope that helps a little other not answering your question, Andy.