This was one of the first errors reported. When starting your next game, please use the biq in post 2 of this thread that holds many fixes, among them the fix for the C47 Dakota, too.
Outposts in my eyes are pure crap. I don´t use them, but they are in CCM 3, as they are in Civ 3, too. So I cannot say if they can detect invisible units. My guess is no.
To detect invisible units a flag different to the invisible flag must be enabled in the editor. Per example workers can detect invisible units (to have a chance against enslavers and holy men), but they are not invisible themselves.
They are simply in the same upgrade chain. There is no advantage in upgrading them, but to have a unit in a special flavor.
This is the normal setting for city walls in Civ 3. In my eyes they are very useful, especially against AI attacks by enslavers and holy men. CCM has no level 3 cities and level 2 cities need a higher population than in normal Civ 3.
The unit values of era 1 units in my eyes in CCM had a lot of balancing and there is no need in my eyes to change here anything. There are many differences in values besides ADM, per example different units have different movement bonuses in certain terrain, elephants have an additional HP, camels have stealth attack and so on. I tried to keep ADM low to avoid an inflation in those categories as it happens in normal civ 3.
If you like those values suggested, please feel free to do these settings for your own game, but please take into account, that you should rise many of the values for the following units in the next eras, to keep here some kind of balance.
You can use different sets of terrain, that you can download in the Civ 3 graphics forum at CFC.