Getting back to basics, For one, Welcome aboard mate. As was stated, the 7z files are the same as winzip files (basically) and if you right click on one, your computer "should" have a generic 7z opener.
Accurate German Flags; If you look at any German flag in your game, the mod is working if the center cross on all the red German ship flags is replaced with a Swastika. This will also tell you that your mod enabler is working correctly.
As far as the rest, slow down, take it easy and have fun modding your game. There will be moments when nothing seems right and then, WOW, your game is ramped up 100%.
You asked for a couple of mod suggestions, one is the latest version of the UI mod you mentioned. Try the "Dynamic Environment" mod found in the Mods Forum, it's great. "Mighty fine crew" is another.
There are so many more, but that's enough outta' me.
Good Hunting, Kaleun
