Giggidy!
Are the Duracons discontinued? There was a weird surge in price, but that dropped (over the past few years). Good thing I got my two knobs for $60 each (at separate times) .
Should depend on the app the radio is using (not that I know about in car Android radios). Both stock music apps on various phones I've owned and Spotify have the 'resume' feature.
Probably the gauge. It's meant to be normalised, meaning it'll sit in the middle for a range of temps (I can't remember what, but there's a write up on how to remove the normalisation so you can watch the gauge move with temperature).
I never had issues with Liverpool exhaust. Just turn up and tell them what you want done, don't ask for advise. Simple and cheap. No issues with their work.