Ok I'm bored at work and will try and help you out here. I'm not trying to criticize you, rather help you out a little.
I would also recommend you join the offsite forum (if it's still working) and sign up for the mentor program. There you can get advice from a number of the top Australian coaches in your own private thread. Somebody also mentioned the Fishbowl PL, find the Australia - IV.7 forums and ask questions in there if you want as well.
1. While having players on your team since they are 18/19 might sound like a good idea, it probably isn't going to work out in the long run. The reason being (and you've already mentioned it) is you can only focus on so many players to train at one time. If you are going to train C's to begin with, that leaves your guards untrained until you finish training big men. By that time, they will probably be 21 or close to it in which the effects of training slow down significantly and it would probably be a waste to even try and train them. Finding a second C to train along side your main trainee is definitely a good idea and you should be able to pick somebody up relatively cheap. You don't need MVP+ potential and you will often find that 18yo with superstar or perennial allstar potential are significantly cheaper than those with a high potential yet same starting skill set.
2. You already have the right idea in keeping your players to roughly 60mins a week, however respectable game shape isn't actually that great. Aim to keep your players in proficient game shape.
3. There are many people who believe 2-3 is actually "broken" and don't advice people to use it at all. I'm sure you can find more info on this if you search but basically man to man is believed to be the 'best' defense against an inside focused team. Using outside based defences (ie, 3-2) can also be used which will stop any passes from being made to the
4. Agreed, shot blocking doesn't seem to be that important and just jacks up the price of big men ridiculously for minimal benefits.
5. Yes basically cross training is where you train one skill and there is a small effects on all the other skills. I'm yet to see any effect of cross training but it's only been around for a season now. The elastic effect is where you train one skill so it is much higher than the others and will then cause the other skills to train faster as they try to catch up to the other, much higher skill. I haven't really read much about this but it was my understand that as one skill went significantly higher than the others it slowed down so I'm not sure how much benefit you actually gain by doing this.