* Open your dump valve on your shoulder all the way
Thats assuming the suit has an auto shoulder dump. A lot of suits still have cuff dumps which makes the dumping task straight forward - just raise arm.
Lobster divers sometimes get turned face down and fins up, while chasing a bug, and if they have a lot of air in their drysuits, then the air could shift to their feet, pop off their fins, and send them rocketing to the surface. In a situation like that, you would have to quickly tuck and roll, vent the excess air, then swim with your hands to find your fins again.
Hmmm. If you have too much air in the drysuit (overweighted then) and you go inverted the air will migrate to the boots and can pop fins off. However if the diver is neutral when it happens (why wouldnt they be?) that wont result in rocketing to the surface - no more air enters the suit, it simply moves.
Anyone getting inverted and losing fins has a serious issue with their dry suit - too heavily weighted, it doesnt fit properly or they cant use it properly, all of which result in too much air being put into the suit - diver error.
1) My trim was not good. I felt like I was swimming a little too head down. Do I need ankle weights or will I be able to make adjustments to this with experience?
Ankle weights are not evil but try the suit without them - you may find you dont need them, they can often mess up trim. If you feel your trim is out, try adjusting your tank position to counter it, eg higher up if head-high and vice versa. Maybe put a small trim weight somewhere to counter it.
Neoprene tends to be floatier than member suits but i still know a lot of people (vast majority) that manage without ankle bricks.
2) How much squeeze is too much?
Totally up to you, its purely until you feel comfortable. If its colder a bit more air in the suit is nice due to its insulation characteristics as well. There is no right amount of squeeze - i prefer none.
As for finding leaks, your method is ok for bigger leaks but for seams and tinier ones my preferred method is to turn the suit inside out as much as possible and fill with water - you can see the water seep through.
AFAIK PADI and BSAC teach people on single setups to use the drysuit for buoyancy and provided they're weighted correctly cant see any problem with this - it saves the task loading of handling 2 expanding air sources of ascent.
Personal preference though on that.