1999 Prado Overheating Prob.

Hi, I've purchased a 1999 Toyota Prado a few months ago & shortly thereafter I got Toyota to carry out a service & they also replaced the drive belts. Whist on our way to a holiday destination we broke down about 700km from home...... the vehicle overheated. Reservoir bottle was boiling. After topping up the needle returned to the normal temperature but after driving a few km's it overheated again. No signs of visible leaks at all but water was going somewhere. I got it towed to Port Hedland where the mechanic attended to it. Replaced the thermostat valve, valve seal, tightened the bolts on the engine block & flushed the cooling system. We continued with a hire car & upon our return we collected the repaired Prado & drove 450KM home, apologies for long explanation but my questions are;
1. Should I get a mechanic to carry out a compression test? (I did drive 450km after the repairs were done though)
2. How often should I replace the coolant (live in the Pilbara & drive the vehicle over weekends)
3. Prior to a long road trip again, what can I do to ensure the cooling system is ok.

Regards.....