My input.

1) Transferring miles does not reset the expiry date.
2) One account for both upgrades, or split the PNR and use two accounts, one for each upgrade. This will be of use if the first account has less then half the miles needed so it'll be cheaper to transfer the required miles to the second account.
3) No idea.
4) Yes and No (sorry). There are Flex Business and Saver Business tickets. Either may be available to purchase direct, and they come from different buckets so availability may change. Upgrades from Y always come from the same bucket as Business Saver Reward so buying an Economy ticket for upgrade requires a different bucket again and may have different availability.
5) Yes. Look on EK site for Business Saver Reward availability and it's the same for Y-J Upgrade rewards.
6) Yes. Yes.
7) They often appear at very short notice but it all depends on how busy the route is at that time. I can't help you there.

Expert Flyer, although not required to check availability, can be handy for alerting you if upgrades are released. With the top level of service you can set it to email you if the fare bucket required becomes available. It saves checking on emirates.com every day.