If you're flying in biz, get to the airport at T-90 mins at the earliest - 7:30. If you have no bags to check, you can even check-in online and get there at T-60. Assuming an hour for the bus (it shouldn't take that long), leave at 6:30-7:00 from Atocha (check the timetable). Another alternative is the metro, though that'll be 1-2 transfers, depending on where you're coming from. Don't take the train to T4, that will be slower.
1. No traffic
2. Assume 15-20 mins.
3. All depends on where you're leaving from.
4. T123 is more efficient than T4 (and faster to get through) but not as nice looking (I'll take efficient over nice-looking any day).