#1
Based on your size...
For non-technical, steel doubles the 50# wing would probably be the better choice. I'd probably get the #30 for singles. Of course that all depends on how much weight you're carrying. your air bladder should be able to make your rig+you positive at the surface.
If you want to get serious abotu technical though, you should be a double bladder for your doubles.
Weight doesn't have to be an all-or-none thing. You can put some on your plate and have some integrated/on a belt.
#2
Never heard of Dynamo, so I cannot compare them to Atomic. How can a 2nd stage be environmentally sealed? If you completely close it from the outside you can't get air
#3
If you're eventually going technical, I would go ahead and take basic nitrox so you can learn more about partial pressures and breathing diff mixes.
In the context of a dive computer, pO2 is the partial pressure (p.p.) of oxygen in your breathing air. So for normal air at the surface (with 21% oxygen and 79% nitrogen):
pO2 = 0.21
pN2 = 0.79
As you descend, your regulator delivers air at a greater flow rate (proportional to your depth). So for example, at 33' when you are under 2x surface pressure, your regulator gives you twice as much air for each breath as it would on the surface. However, that air still occupies the same volume (your lungs + dead air space). So you are breathing air that is twice as dense as on the surface. Since there are twice as many molecules of O2 and N2, their p.p. doubles, so:
pO2 = 0.21 x 2 = 0.42
pN2 = 0.79 x 2 = 1.58 @ 33'
You can see that the deeper you go, the more p.p. increases. You reach a point where pO2 can be too high that point is different for each person and even for the same person depending on your body that day (dehydrated, etc). A high pO2 won't really be harmful short-term, in-and-of-itself. But too high pO2 can cause you to have a seizure underwater. And that can lead to drowning.
Consequently, many of the training agencies recommend that you don't exceed 1.4-1.6 pO2. This will be explained further when you take a nitrox class.
Your computer won't measure this value from your tank. You would set it manually after analyzing your mixture before diving.
I am not familiar with the Vytec or EMC-16. The VT3 is an excellent recreational computer. It is air integrated and can handle nitrogen loading for nitrox up to 50%(?) O2. It can also handle up to 3 mixes if you get more transmitters. It should hold up very well within these parameters.
However, most technical divers tend to plan their dive profiles and nitrogen loading before a dive and go with a computer that can handle Nitrox up to 100% and are not air integrated. The Nitek series is a very popular one.
