I think you're close, but 1) I think we're getting Dark Avengers, not Thunderbolts, and 2) I think they'll be setting up a Dark Avengers team that's an inverse of the original MCU Avengers.

Here's what we know so far:

1. Skrulls have infiltrated earth (with Sharon Carter appearing to be taking the role that Spider-woman played in the comics) and is building to Secret Invasion
2. Contessa Valentina is gathering a Dark Avengers team (starting with US Agent). She appears to be functioning in the way Victoria Hand did in Dark Avengers.
3. Post-Secret Invasion, Contessa Valentina will make her move, the way Norman Osborn did, to establish herself as the new director of SHIELD with her own team of Avengers. She'll be gathering a team throughout Phase 4, the same way Nick Fury did during Phase 1.

Based on this theory, I think we'll be getting the following team:

• US Agent - dark version of Captain America
• Yelena Belova - dark version Black Widow
• Red Hulk - dark version of Hulk
• Taskmaster or Bullseye - dark version of Hawkeye
• Loki - dark version of Thor
• ? - dark version of Iron Man

For Iron Man, we don't know who that will be yet, but there is an upcoming 'Armor Wars' Disney + series with War Machine dealing with Tony's armor falling 'into the wrong hands'.