Does anyone know of ANY walkthrough help out there? I'm all googled out. This one seems A LOT harder than the previous three.

Hmm.. there is dozens of German walkthroughs as one might expect. You could search for 'brainsworld siedler 4 lösungen' and let google translate it for you.

Haven't played this game in ages, but I also found it pretty challenging back then so I've never completed any campaign :)

OH MY GOD!
YOU'RE A GENIUS!
YOU'RE THE SHIT!

It actually looks like I was also doing the missions in the wrong order, if you saw the S4 menus you'd understand. What I thought was Mission 2 of the whole game was one of the LATER LATER LATER missions meant for people who have breezed through most of the rest of it.