Hey there, TPG. Welcome. Let me see if I can answer these for you.
1. I think that is roughly correct. So I read. That always confused me in the beginning. After getting into it, I realized though that you wind up
vaping much differently that smoking. Smoking you take a break every once in a while where you might wind up
vaping here or there all day. Drag here, drag there. Supposedly, the amount of drags off of a full carto is about the same as a pack of analogs. I can say that I smoked about a pack a day and now I do go through a filled carto every day. Some people really get these cartomizers or atomizers to last a long time, but personally I don't like when the taste starts to change so I use a cartomizer for a week then replace it. I use an atomizer for a month then replace it.
2. This one is hard to say. The answer may exist somewhere but i've never seen it. I can tell you this. I've never had juice go bad. Some people like to let it sit around to "steep" before using it even. If you want to keep juice for a long time though, refrigerate it.
3. I won't say definitively but from experience, I've never seen that have a noticeable effect.
Please post as many questions as you have. I'd love to help.
Also, please check this out, you may find it helpful even if you're not using MV.
http://www.e-cigarette-forum.com/forum/modernvapor/214136-modern-vapor-hardware-basics-tips.html