Just to note, OP said he has built about 10 rockets but has not used a motor bigger than a C.
I'm surprised no one has brought it up yet, but another good idea would be for you to download OpenRocket and try it out. Experience with simulation software is vital if you intend to get serious about the hobby. At the very least, OpenRocket or RockSim will help you match rockets to motors they can fly on safely.
The questions the OP is asking don't indicate even that level of experience.
Built "about 10"? Perhaps.
Flown 'about 10?'... the OP's questions definitely don't imply that.
for example, i't's probably safe to say that most of us knew at least the basics behind motor eject-delay time within the first few flights ever.... (back in our "rocketry-infancies!") (I was 10)
OpenRocket/RS is a good idea, but they still don't replace basic, ground level experience. OR is great, I use it a lot. But one has to have enough experience to look at the output and say: "...Hmmmm, that doesn't look right," or "nope, tolerance to x is to close/far-out"
Kinda of like current California primary school Math these days... they teach with calculators... some of these kids punch in some number, and get an answer, not thinking that it doesn't make sense. (3 x 3+(1-2)= 432..... (uh... NO)
Gotta LEARN the basics: SLOW DOWN, Read, and then go fly *different* C motors, and A, and B, and then a Ds... Then he will have a better understanding of, and answers to the questions has asking, not to mention the data from OpenRocket / RockSim.
(And the OP is asking about E motors, so, we did not in fact jump to fast!... )
