Getting back into collecting! Could use some help!

I haven't purchased/collected comic books in at least 20+ years. I loved it as a kid and have been wanting to get back into collecting since peak MCU. I've got a good friend who has recommended ~10 runs that I check out, just as a starting point.

After a few years of just randomly checking out comic book shops to see what they have, I have finally found some issues of Nick Spencer's Captain America: Steve Rodgers. (Couldn't believe my luck finding a shop that had issues #1-11 original covers!)

But I am coming at this as basically a newbie. So I have a few questions:

1. Is there a set timeframe for how long new releases are regularly stocked in stores? I know Spencer's Steve Rodgers run is over 10 years old now. I'm sure Marvel is not constantly printing and stocking stores with new copies. Basically when a new run starts, and an issue is released in stores, how long are they getting sent to stores for? Until the next issue is released?

2. I don't want to do trades. I love the comic book format and want to stick strictly to that. Is my best bet for finding some of these older runs literally just checking out as many comic book shops as possible? I'd prefer to buy from shops and support their business, but if some stuff just isn't in stores anymore, where else can I purchase from?

3. Spencer did CA: Steve Rodgers and CA: Sam Wilson. If google is correct, they were released somewhat side by side. Are there comic book runs before or after that are necessary to understand this specific story? How do you determine what you want to read/collect and not?

4. Any tips/advice in general? Sorry if my questions don't make the most sense. Like I said I'm just getting back into this and trying to learn as much as I can. THANK YOU ALL IN ADVANCE!