planning on buying first AP so a few nuts & bolts kind of questions
1. what is best way to purchase, read something about upgrading on last day of trip to AP, how to do & advantage of it
You can buy the AP outright up front, or you can upgrade a different ticket. The benefit of upgrading a ticket would be that if you buy it, use it once to enter the park, they will credit the gate value of the ticket. If you try to upgrade before use, they would only credit you what the reseller paid for it. You would need to buy the ticket from a 3rd party that charges less than WDW for this to be beneficial. You would want to purchase a ticket that has the greatest discount, without costing more than the AP. So the current gate price for an AP is $675.21. Undercover Tourist currently sells a 6day hopper + WP&M & No Expire for $577.47, which is $72 savings off the gate price of $649.75 (tax makes the numbers funny). If you that ticket from UT and use it to enter a park once, and then upgrade it, you should be credited the $649.75 towards the AP. You would need to pay the $26ish difference between the two tickets, but you still end up saving a chunk of change. You may need to ask the CM at Guest Relations to "bridge" the ticket, as some may not automatically credit you gate cost. Know what the numbers should be, and don't be afraid to ask them to double check if they sound off. If you buy a ticket that has WP&M on it, and use that feature, you would need to upgrade to a PAP, so just keep that in mind.
2. how are wristbands & FP+ handled
AP holders are able to order a free MB via MDE after they activate the AP. If you are staying on property, you can use that MB, or you can buy one in the stores if you need to have the MB right now, Otherwise the card they give you when you purchase/upgrade to the AP will be RFID enabled and would work for FP+.
If you buy an AP online, you will get a number you can enter to book the 7 days of FP+ online up to 30 days in advance. If you buy tickets to do the upgrade, you can book FP+ for as many days as the ticket allows you. Some people choose to save less money to be able to book more days worth. For instance, the numbers I referenced above were for a 6 day ticket. So you could only make 6 days worth of FP+ bookings in advance. Once you convert your ticket to an AP you can only book up to the 7 days an AP holder is entitled to. So you may choose to buy a 10 day ticket, and then upgrade on the last day allowing you to make 10 days of FP+ reservations the 30 days in advance.
3. how often are rooms discounts for AP issued & how much are they usually
All over the place. You can see past release dates here ->
http://www.mousesavers.com/historical-information-on-walt-disney-world-resort-discounts/ They may be only 5% off, or they may be 35% off. Depends on how many rooms WDW wants to fill. It may be slightly better than the discounts offered to Visa holders to the general public, but may be released on a later day.
Some. You can get an idea of what may be offered here ->
http://www.wdwmagic.com/other/annual-pass.htm I do strongly advise against counting on any discounts, room or otherwise when running breakeven on the AP. As evident by some of the recent postings about mini golf and boat rental discounts for APs being slashed, they may disappear at any moment.
5. is spur of moment trip now just get room & go?
For the most part. The only other thing to keep in mind is going to be FP+. You can definitely go down and enjoy some rides, but if you want to get on 7DMT, well you would more than likely need to wait in the standby line as the FP+ may be long gone.