It sounds like you have a lot of ground to cover with the basics of audio electronics, and reasons why traditional material choices prevail in manufactured and DIY electronics. Shielding, heat transfer/removal, electrical safety, grounding and fire risk are all part of a long topic there since the scope of your question, even on the surface, is immense.
It also makes a big difference according to the size, power source and output requirements as to what options are realistic or just wishful thinking. I suggest you look at a few more threads where the guys are building something that you think is within your capability and interest and work out some specific questions with that model as a basis.
Then, might I suggest you also read a proper text on amplier design such as those by Randy Slone (beginners). Bob Cordell and Douglas Self (advanced). or the articles on this website. Think about something we can answer simply without needing to quote endlessly and virtually write another book with a paragraph from everyone who happens along. It's interesting that way but you learn more and consistently from a well written text.
I am trying to stimulate discussion. What is your preference when you build an
amp? Aluminum is the choice of builders. Why? What kind of capacitors do you
use? Auricap? Solen? Something else? Resistors, diodes, wires, transistors,
transformers? Are the parts you use in your project better then those found in a commercial amp? What kind of volume control do you like to use on a preamp?
Once you reach a certain level of quality, it's all a matter of taste. A dozen people would give a dozen different answers...
Dale RN series are very good metal film resistors to use for anything. I use RN55 and RN60 all the time. Other manufacturers make RN types as well, like IRC. The RN designation means they're Mil-Spec, which doesn't necessarily mean they're better, it just means they are manufactured to conform to a specific set of standards which have proven to be reliable over the years. Therefore, I like to use RN type resistors because I can be assured that they will meet a consistent good standard of performance.
Standard commercial quality components, each selected by type, to suit the duty in their part of the circuit will give very good performance.
Provided the components meet the specification that determined their suitability.
Metal film resistors, electrolytic, film & ceramic caps, transistors all must meet their specs.
None need to be special audiophile types for very good performance.