I'm really not sure about the campmap zoom, I tend to favour the mousewheel so haven't really looked for alternatives...

For your other questions:

1) Using the Merge command usually spreads your generals around the stacks, it doesn't make them disappear! So if you have two stacksworth in a province, and start with say your king and a reasonably high command prince in one stack, afetr hitting M you should find the prince in charge of one stack, and the king in the other. Commanders will ONLY appear in the Military Parchment when they head up a stack, so if all your princes are stacked with your king, they won't show. Even if your princes did die of old age, the unit will still be there, just with a replacement "commoner" in charge, although unless you're using the "green generals" setting, his stats will be exactly the same. I don't know where your princes went, they don't just vanish like that! (Sure you haven't had a wave of enemy assassins???)

2) Only the stack-leader's stats affect the whole army - his command stars add valour and his v&vs will modify morale (if he's a screaming wussy-girl, then his whole army will be, too.... ) Giving him a second in command has no effect! Loyalty doesn't figure in battle, only in the case of bribes or civil war. Beware high command low-loyalty generals. They can rebel, especially if you put them in charge of a large stack. Loyalty will improve for all generals as your king's influence improves, or he gains virtues like "builder" line etc. Disbanding disloyal units is just a waste of cash, really.... put them under a loyal general, then they can't do any harm. They will improve with time and your king's prowess. The higher his influence the higher the loyalty of newly trained units, too.

3) Increase command by winning battles. Only applies to the general. Individual units in an army can gain VALOUR by making kills in batle.

4) To merge units they must be in the same province at the start of a turn. If you move one unit from say Mercia to Wessex, it can not merge with the Wessex army until the next turn.

5) Is bit of a bug - rest assured if they get into a battle the most capable leader will be selected whichever one was added to the stack first or last.

Hope you get this before you rush off home.... I'm also waiting the end of the day to rush off home back to MTW-land