There are hotkeys for each type of minion - however I just use M and manually issue orders on the field. Knowing how many minions you have active, though, isn't easy - there are no indications to tell you, so you just have to keep an eye on your minions. I'm hoping this changes once we have offical mod support.

as sedna i only use select hero only, select all minions only and select all bounded to some mouse buttons. i usually only have priests/bishops. on other generals it may makes sense to split the control of minions and special minions .eg. using erebus or oak as their minions are melee.

First :
Play a lot with h (only dg), m (only minions) & n (all). o stands for 'all minions come back close to me please'

Then :
You need to master the selection with double click (select all minions of 1 kind), because you want your archers attack the tower, you priest stay back and your yetis ( ) to tank.
Forgot keyboard shortcut because using them you are forced to keep all your minions in the same place. Send 1 or 2 nightcrawlers for fogbusting, send your archers on a tower and send a priest on an ally DG. Then you must click and drag to select your DG and the remaining minions.

If you use 'M' or 'N' or 'O', you will loose the specific order given to your minions.

Remember minions do collide with creeps, you'll find it hard to sent a shambler in the middle of an ennemy wave and make him blow.

This game is done so that micromanaging minions is hard, and it is a good thing. It prevents good players (not pros) to overwhelm with extra micro. Samely you dont have to deny your creeps to the ennemy. All in all this make the game a bit frustrating sometime (because you can not use your minions in an optimal way) but it is a good thing.