Firstly, I must say it would be an honor to assist with this as something of a history nerd. It sounds quite interesting, and something that might be good.
Secondly, I want to say I am very damn concerned. Being anti-Nazi did *not* make one a good guy, and in fact most of the A-listers we know of (Rommel, Stauffenberg, etc) absolutely were not.
Really, when you boil it down, huge gobs of the German “resistance” were basically as totalitarian as the Third Reich was. On the far left, you had the German Communist Party (or KPD), who were more or less the harbingers of Weimar’s collapse and who practiced the sort of bloody street thuggery Hitler and Roehm used without the political savvy or ideological willingness to use the electoral system to subvert it.
On the right, we more or less had the loyalists of the Second Reich, which was noticeably better than the Third, but *not by thaaaaat much.* They were more or less supporters of a very reactionary, very brutal autocracy that would allow themselves expanding markets, estates, and territory on which to build their dynasties, all those who had to die or be enslaved to do it be damned. They willingly engaged in genocide (case in point: Germany’s African colonies, the attempts to crush the ethnic Poles, the policy in Alsace-Lorraine after 1870, and general occupation policy overall), coverups for genocide (case in point: the Ottoman Turkish Empire, the Habsburg occupation of the Balkans- especially Serbia- and what have you), flaunting of any form of reform, and crushing those who resisted. After the Bismarckean Empire was defeated and destroyed, they then promptly began to wage war on their own people, the left, and the Weimar Republic itself, to the point where the German Military sanctioned or abetted so many coup attempts it is downright insane and the times they *did* act to protect Weimar were less because they accepted it or supported Democracy and more because of pragmatism. (They did not want a far-left dictatorship replacing Weimar because it would obviously hurt them, they largely believed the Kapp Putsch was premature, and the opposition to the Munich Beer Hall Putsch was more because Hitler’s Co-Conspirators in charge of Bavarian politics decided to leave him out and Hitler acted to force their hands). Rommel *absolutely was* one of these people, and it shows.
And then you have the unholy hybrids where Far Left and Far Right meet, like Stauffenberg himself (who favored allying with the Soviets to cement control over Central and Western Europe by war if need be) and Otto Stasser’s Black Front (basically surviving Roehmites and the more revolutionary left wing of the National Socialist party like the guys who got axed during the Night of the Long Knives).
Let me be absolutely clear: These people DID NOT support Weimar, did not support Democracy, and Did Not support Peace. They differed from the Nazis mainly in ideological orientation, bloodthirstiness, populism, and pragmatism. Under different circumstances they could have been responsible for as much misery as the Third Reich ever gave out, and they came very damn close in WWI and the years before it.
That is why I take offense to any idea that the Regular German Military (or rather, the established/“standing” parts of it, especially the officer corps) were in any way the “Good Guys”, believe that any idea dealing with the German Resistance has to deal with it tactfully in order to avoid twigging my moral and historical sensibilities (and I imagine I am not alone there), and in particularly believe Rommel and his ilk should have been hung until dead in a public place for being the willing handmaidens of tyranny and allowing into this world great crimes that could have been prevented. Great crimes that often pre-dated Hitler, and set the stage for his rise.
Rommel wasn’t a monster, but he certainly was not a hero, and you should be aware that what you are describing for the protagonist has little to no relation to him (again, Rommel was an aristocrat, an officer, a member of a military dynasty, *commander of Hitler’s military Bodyguard*, a doctrinaire monarchical absolutist, and a despiser of Weimar).
I’ll be happy to help however I can, but I want to make it absolutely clear that whitewashing- or its’ uglier twin, blackwashing- is an absolute no-go. The German resistance groups were never monolithic, and I mainly described the “Bad Actor” factions (and even plenty of those were legitimately disgusted morally). However, it would be a great offense- coming near the centinenial of the first Great War- to forget or paper over the origins of a lot of said Third Reich (and the problems with German political culture in the Second Reich), the less than noble ideals of many subsections of said resistance, and how the military (*especially* the military aristocracy like Rommel, Canaris, Stauffenberg, etc) served and duly enforced the bloody rule of not just one but two totalitarian governments over Europe, and fought to protect and expand them in two bloody and traumatic world wars and otherconflicts.