@pete, here is a screenshot of my first turn. It should be noted I was able to get a gold star.
1st turn: Focus on breaking the megabonus of Marshall Wihelm and Capt Stygr. Since the income of everyone is around 40-50, just focus on having enough defense to hold the megabonus on all other fronts (65 should be enough). You can refer to the screenshot to see my deployment to get an idea. https://prnt.sc/ok480q
2nd turn: General Correia will likely break in (that is okay, if he is the only one). Focus this turn on breaking Colonel d' Orglande's Megabonus and put enough units to seize a few (2 or 3) territories from Wilhelm and Styrgr who have been breached.
3rd turn onwards: Focus on Major Brennar and break the megabonus for him and General Correia. From there, you should be able to sweep the challenge
It should be noted for your first turn to have the 50s attack the Maria ship as your first two orders and the attacks on Wilhelm and Strygr as the final orders as they have quite a few units (it may be possible to avoid General Correia breaking in on turn 2 if you, combine your two 50s near general correia at the end of turn 1).