All you are talking about is explained in full game guide which has a link inside HOW TO PLAY section.
Just some of towers can shot over walls, same happens with units. This is part of the strategy when you play.
The orange bar is the current level of the unit, while the white bar is the experience of the current level. The green and blue bar are the current hp of the unit.
150 range is a indication to know how far a unit can shot, if you want an exact quantity it is 150 px in the game but that info is shown just to know if a unit has a high or a low range. Same happens with an unit speed, reload time, etc...
About wall construction, yes it can be improved but in many rts you have to build the walls this way.
IA looks for you when you attack his base (except on first map which is a tutorial). If you attack other zone of his base the IA will go to defend that zone. IA isn't stupid like shit ;) Try a high efficiency playing at beyond zone 5-6 (winning those maps won't be as easy as winning on first zones) and then tell it if you want, the game has a lot of work and it has been tested several times.
All of this is explained on the full game guide, which would be too long to put it on game description.
Thx 4 all your comments.