(1) You'd have a difficult time showing the dependence of John on Mark, and John also has Peter's denials. That work claims to be based on an earlier work by the beloved disciple who is depicted as separate from the later apostle tradition within the work, so there may have been an earlier narrative work both John and Mark share, absent the sayings work Mark would have been relying on which is one of the places it differs noticably from John. I agree that Mark is largely written to set up Paul (if you haven't, check out Dykstra's Mark, Canonizer of Paul), but given Paul's claims are that Peter directed him to the areas he was active in and that he had studied under Peter (but no one saw him except James) in Gal, the work still needs to prop up Peter as the successor who then passed things on to Paul.

(2) Where is Mark 4:3-9 in Elijah? Or Mark 13:1-2? Both public statements that are expanded upon in private instructions in the text. These were very likely known to the audience Mark was being written for and proceeded the work in saying form, which is why it characterized them as being said in public while trying to spin them with the private parts (which it should be noted may well be a later reactive layer to Mark anyways). You might find it interesting to reread Mark closely paying attention to when it breaks off for private instructions or secret disclosures (such as the secrecy around Messianic claims - claims completely absent in something like Thomas).

(3) Correct, the empty tomb was likely a later embellishment, which would make sense given Paul himself likely developed a lot of the eschatology around resurrection and a sin sacrifice. The Corinthian Creed did possibly predate him, but even then it would have only been a core part of it, and Paul expanded on the mythos quite extensively. It's not that Mark is introducing the empty tomb that's remarkable, it's that he's having his only witnesses not tell anyone about it. You see something similar in John where Peter and the unnamed beloved disciple race to the tomb, Peter loses the race, but then the other disciple doesn't go in. There was clearly an effort to try to fit figures like the women or the unnamed beloved disciple (who takes the women into his household at the end of John) into an empty tomb narrative as silent or reluctant witnesses, which would make sense if a competing tradition connected to such 'superapostles' wasn't saying anything about the tomb or resurrection.

all 4 quests have failed

Quests? Like Arthur and the holy grail?

you can deal with actual scholars not amateurs like me who suck at Greek.

It was pretty awesome spending nearly every day for years participating in /r/AcademicBiblical alongside PhDs and very knowledgeable fellow contributors. I definitely learned a lot, and was honored to be labeled as one of the sub's Quality Contributors (their label for a handful of participants without a Master's or PhD who had high quality comments or posts). But unfortunately Reddit administration killed a good thing with their greed, and now I'm on Lemmy and probably won't be back to Reddit again.

If I do get around to a video series one day, the network of some of the people I befriended in that sub who produce the same kinds of material will be a good sounding board though - it's one of the things motivating the eventual effort.