Change it at the interval recommended in your owners manual. Every 75,000 miles is what most recommend.
Transmission fluid will last roughly 70,000-80,000 miles so anywhere in there.
between 5 and 6 qts.
For best service and durability, 30,000 miles is recommended.
You do not need to worry about that. Toyota uses stable transmission fluid that can last way pass 150K miles. Unless you have problems with the transmission, you do not need to worry about it.
5000
6.9 with pan removel
According to\many websites you should change it every 30,000 miles. But if you have Dexron III ATF which is supposed to be good for 100,000 miles. You can also change it if you just want to.
On my 2000 automatic 4WD, I have to drop the pan to change it. It is designed as a sealed transmission and is not supposed to need changing all that often.
I have a 2005 Sorento with 104,000 miles. No issues. I do change the oil, transmission fluid, and other regular maintenance. I hope for over 200,000.
There is no way to tell how long it will last. If you change the transmission fluid every 75,000 miles which is what I recommend, and do not pull any load, it can last as long as the engine will last. It may also fail with less than 100,000 miles on the odometer. No way to predict how long it will last.
5 quarts for the auto transmission. However, if you have a high mileage transmission, +75,000 miles, then use an additive such as Lucas in place of a quart. Ixnayer