Is it advisable to warm my 2ltr van up before I jump on the freeway and do 80-90 km/hr. It only takes 2-3 from my home before I get on the freeway and I hope I am letting her warm up enough. The motor was rebuilt 2 years ago

This is one of those topics evenyone has there own opinion on, and are all certain to be different.
I suppose firstly, do you have the original thermostat hooked up? If not a decent warm up time is recommended. If it's working correctly it helps the motor to heat up quicker.

I personally give the car a good warm up. I'm in the habit of starting the car and let it warm up while I load tha car, lock up the house, open the gate etc..... ~2-5 min. Even so on a 20 deg morning the heads get to operating temp after ~10 min. driving and the oil takes ~15-20 min to get to 70 deg and up to 30 min to level out.
I don't have the thermostat connected at the moment (the copper thermostat is cracked) but will fit a new one before winter.

My thermostat is not attached due to the temps up here in Brisbane

Yes, most have them removed nowadays. As I said, every one has there own opinion. My dad starts and drives off, no warm-up (all H2O vehicles), and doesn't seem to affect them.
I'm in Brissy also!!!