1a. You can certainly order tickets separately from your resort reservations.
When you order non-package tickets, you pay at the time of the order.
1b. You can make three separate ticket orders.
1c. Yes.
1d. Yes.
1e. Likely, but that's not a problem, either way.
You can freely transfer any new tickets over to other guests in MyDisneyExperience.
2. Yes. (Or, likely it will automatically link to you.)
3. Non-expiring tickets are no longer available.
Thank you!