With the exception of combining some answers for brevity, the questions and answers are exactly as quoted in these sources.
Allied units start next to the area they enter.
This comes in handy when some units are skulking in towns and some are not. No, the defender chooses which units will take hits within the one hit rule. Note that if the unit inside the city is eliminated, the remaining rounds will be without the city defense effects. If the unit outside the city is eliminated, the attacker will be able to advance and encircle the city. Does not effect units without hits.