Right Hook/Overhand right

You're right, the right hook does leave you more wide open because like a straight right you have to turn your body and pretty much square off in front of your opponent in order to throw it.  That's why you have to be selective when you use it.  As well, you can still protect yourself somewhat using your left by bringing it across your face to protect the right side of your head.  To throw a right hook, you are pivoting on your back foot with much the same twisting motion as a straight right only a bit more.  Your fist orientates itself the same way as if you were throwing a left hook.  I'll try and get some more video up on the site shortly...

As for an overhand right, it's a finishing punch.  You ONLY use it when there is no chance of counter-attack because you are pretty much opening yourself up completely and throwing every bit of weight you have behind it.  It's like the punches most people throw in street fights.  You wind up and hit bringing your fist down through your target.  You are committing yourself completely, weight transfer and all, so if you miss you will be off balance and you will be open for a beating.  It is very easy to see coming as you are telegraphing it right from the start by drawing your fist back and starting the looping motion.  Unless your opponent is too tired/slow to get out of the way, it will not be very effective.  If you do connect though, it will hurt.  I'd worry about getting everything else right before packing this one into your arsenal.