[flamingo]

1. The pond would be fine as it's fully grown.
Larger is always better though. He should be moved over well before he/she reaches 6", a 20g would suit a hatchling.

2. Preferably, all aquatic turtle tanks should be barebottom. It's much easier to maintain, since you'll be doing water changes every few days.

3. For the basics, use an internal filter, a basking light with good UVA/UVB qualities, a sectioned off heater if needed, and a basking area.

4. They'll eat pellets, possibly veggies such as romaine lettuce, spinach as a snack, collard greens, earthworms/leafworms, feeder fish, fruit, and probably hundreds of other things. They're more carnivorous when younger.

5. Around 76 or so should be fine.

6. You definitely wouldn't want to keep them with newts.

Just remember they're "fairly large" as they grow, and need a large area to swim- I've seen them do well in 150 gallon tanks. Be sure to change the water often, smaller tanks should have daily or every other day 50% changes. Otherwise, you could potentially stunt the turtle, cause shell curl, eye infections, etc.
HTH