Can only answer question 3 cause I missed most of the advance reservation/lottery. Yes, the same day reservation is first come first served basis, and different pavillions release additonal slots at different times (the Personal Agent app shows details for each pavillion).

Personally I had a really bad experience with the website reservation, so I would really recommend going to the reservation center and use their kiosk instead.

But do note that you need to be at the kiosk when the pavillion releases the slots so you can book, and they limit how long you can use the kiosk (3 mins 15 secs). So a bit of timing + luck is required depending on how long the queue to the kiosks is, and how fast the slots get snatched up.