I partially agree with most of your points.
1. I don't know if he'll have to go after an IG unit. I assumed the circuit board is a MacGuffin, don't know if it will tie into IG-88 specifically or some other character. I assume that he'll ahve to free Gideon to get the part.
2. For sure the Pirate King is a pawn for Thrawn, I'd bank on it. We know the Empire often tied themselves with Crime Syndicates to partially control the outer rim.
3. Bo Katan could easily be a villain. I think she is there to act as a potential bridge between the Children of the Watch and other mandalorian factions. I suspect there will be a large Mandalorian conflict. Maybe not coming to blows but certainly a heavy test.
4. I don't think that's true. But maybe it is.
I think my favorite theory is that Grogu will claim the Dark Saber after someone takes it from Din and become the new Mandalore