***When I built an outpost with only one square of forest in reach, I could build the initial mill (or whatever it's called), but then it never gave me the option to upgrade that building (and it did for other cities near more forest--this is a guess at the reason of the problem).  On a related note, I see the final buildings take more commitment to build (15-20 turns in a built-up city), so be careful you don't make them so steep with so little benefit that no one will even build them.  I noticed several "upgrades" were, in no way, worth the commitment to make them (especially the "20% when idle stuff" for something like gold which is usually around 5 or 6 for a large city).  There is a fine balance there somewhere, so please keep searching diligently for it.

***One enemy city I captured had another enemy army stuck "inside" the city tiles, and attacking them with my full group led to a battle with my sovereign only (it dropped the rest of the group, and yes, I made sure I did not have him highlighted individually).  My guess is the game put my group inside the city before carrying out my attack order using only my leader.  I attacked them from outside the city--I have no idea if this would have happened had I already been inside the city and manually selected all my units before giving the attack order, but it's worth making sure no enemy groups get stuck like this, or at least that they are able to be fought normally.