Hi Mick,
Unfortunately (for you) the two airports are at the opposite ends of town. At 7:30 traffic will be building up so it can take anything from 45 to 90 minutes. Make sure your taxi driver takes the express way (inform him that you want to go this route and pay the extra toll). Expect longer during the day.
The new airport is reasonable efficient. On the early flights expect a 30 minute wait at immigration; bags are normally waiting for you when you get through. (This gets a lot worse during the day)
Personally I would leave a little longer than 2 hours for the internal transfer unless you are travelling on one ticket for the same airline. If you are delayed by one hour or more then you probably won’t get to check in and board on time. Air Asia do a 9am and 12am flight which might be more convenient.
All in all if everything goes OK then your plans will work but one slip up and you are pushing it!