Hey Brummbear,
first of all: big thanks for your detailed post and the bug reports. This really helps me improving the game. I spotted the building bug of the quarters and (hopefully) completely fixed it. Also the bug which occurred when equiping weapons has been removed. I think, the bugs of being able to build pikeman and the wrong assignment of the building progress percentage have been triggered by the initial quarters bug and do not exist if everything works fine. At least I tried my best to reproduce them and Bad a look into the code once more, (fortunately) whithout success.
Concerning the idle workers which failed to get to the keep building site: A wrong placement of streets may have been the problem. Simply just drag some new streets on the old streets or try another route. Should solve 95% of all pathfinding problems. I'll fix that later.
I'll upload a hot fix tomorrow.
Cheers.