Not if he decided to go adventuring/volunteer fighting against the Nazis on his own while still a prince. If needed, there are ways to handwave this, but, either way, we do not really need to definitely set up other heroes.
Anyway, while we still can't vote, my thoughts:
[ ] [Behind Enemy Lines] Steve goes rogue on his own to rescue Jim from the clutches of HYDRA, avoiding Bucky so that he doesn't rope the young man into this. However, unbeknownst to him, Bucky's already gathering a squad of soldiers to assist Steve in his unsanctioned mission.
*This will establish characters for the Liberty Legion as already being gathered around Bucky and Steve.
[ ] [P.O.W.] There are cameos of other Marvel characters in this base. Write down how many and who they are.
*Not going to focus on that one right now, but Wakanda-related character is a must, the rest can be Golden Age heroes of one's choice, but PLEASE don't turn mutant characters into inhumans. They (like the Eternals) are a specific setting with its own atmosphere, that shouldn't be used as "our X-Men".
For synergy, we can use the counterparts of characters seen on Spider-Man TAS at the time.
[ ] [The Head] Johann Schmidt, the Red Skull. Horrifically disfigured and grotesque as the comic portrays him, he is one of Hitler's private confidants and the leader of HYDRA.
-[ ] [The Head] However, the 1940s Zemo and von Strucker can be present as background or secondary characters in HYDRA leadership scenes.
*He is less HYDRA-centric than the others, but this is pretty much the only time it will make sense to introduce Red Skull, the Cap's archenemy, for it to make sense (
and he fits the logo of that time), others have a better line of successors. Especially Zemo. However, we can still add the predecessors as more "background" HYDRA characters. Maybe make it so Schmidt is not the "Supreme Hydra", but HYDRA's main liason to the Nazi regime, and introduce his Japanese counterpart.
[ ] [Tales of Suspense] Jim Hammond is no longer human, but a brain inside a robotic exterior crafted in eerie lifelike fashion to a mortal man. He possesses pyrokinetic abilities and displays no emotion whatsoever.
*We'll need some ILM-level mastery for this, but anything less would be a disservice.
[ ] [The Shield]
Classical.
*I think we can make sense of it as a re-painted trophy German nobleman's shield. When we introduce Cap into the modern storylines, we can have the Wakandans award him with the Modern shield as thanks for saving their prince/king.
[ ] [Placeholder Name] The Torch.
(Marvel Exec Roll)
*It's not a huge deal, but if it is allowed, it's good. If not - not a big deal.
[ ] [Liberty Legion] Yes, other metahumans that join Steve's squad, several being notable names from the comics but don't have a large role beyond that.
*The
Spider-Man TAS guys I mentioned, plus, possibly, the Black Panther predecessor.
[ ] [MacGuffin] This might need something more fleshed out. Maybe the Spear of Destiny?
*Fits the Nazi era and has some established background that the viewers can recognize. We can always say that the "Cube hidden inside it powered the Spear all along" if we really want to connect it to the Cosmic Cube storyline later.
[ ] [War Assets] By this point in the war, the Allies and the Axis are at a stalemate due to the metahumans on each other's side. For the Liberty Legion, there exists HYDRA's empowered superhumans. Until a solution is found, the war will slowly become one of attrition.
*Doesn't quite fit Marvel's "world outside your window" thing, but this is a much more interesting plot.
[ ] [First Contact] Reports of HYDRA attempting to clean up an excavation center send Steve and his squad in to investigation, only for it to be a trap where the first German superman is waiting for them: Master Man.
*Since the director is looking for an ambush
[ ] [Turning Point] At the height of the battle, Bucky pushes Cap out of the way of falling debris and is crushed to death, filling Steve with trauma at being the reason for his best friend's death.
*A no-brainer, I think.