Dedicated lines — how many? Other advice?

(b) How many dedicated lines for the audio alone? How would you group components on each line?

One. 20amp. 10 gauge.

It’s probably not much more expensive to run two dedicated lines than one, so I’d run one for analog and one for digital for the dedicated audio only. I wouldn’t bother with the A/V stuff — just get a good power conditioner with surge protection with power regulation to protect/prolong their less-robust power supplies and electronics.  FWIW.

Use one direct (dedicated) line for the audio. This will be your high end system line. Everything connected to this system must be plugged into this circuit. Nothing else. This is to a) provide the best power and b) avoid ground loop hum and other noise problems.  

Everything else can be on as many circuits wired however you want. I would recommend one circuit for lights, one for all other outlets, and plug all the other stuff (video, etc) into those other outlets. 

Do not use more than one line for the audio. Use one power conditioner and plug everything into that one AC source. Does not matter how you group components. (There is a lot of misinformation around all these topics. Study my system. See who has what experience. Nuff said.) 

Skip the surge suppressor. Waste of money.  Spend it where it will do more good. Get the Decware Zen https://www.decware.com/newsite/ZLC.html

Use 10awg wire, 20A, and do not stress the details. For what you can spend on stuff you will never hear you can buy one fuse that will make a hundred times more difference. I know. I have wired my room several different ways and heard what all these different things actually do. There is more benefit to a good AC outlet for less money and work than what you can do paying an electrician, trying to convince him, etc.   

Try and keep some perspective. The single biggest improvement by far is to run the one line direct. Otherwise, electricians will always wire a circuit to go from outlet to outlet in a daisy chain of connections. Eliminating all these connections is by far the biggest gain. I have wired my room at least three different ways, including ripping it all out and having all the wire cryogenically treated. By far the biggest improvement was that first step of running the line direct. So do what you want but realize there are things that are extremely cost effective, and then there is a lot of other stuff that you could do way better with the same money any of a dozen other ways.