Welcome aboard forlorn..
You could call your local Pontiac dealer and ask what their recommended service intervals are and schedule accordingly. IMO... buying this car used with 16K, you should be ok, check the fluids for abnormal color etc. My clutch fluid was filthy and was changed out at 26K under warranty. I could wipe dirt residue from the inside lip of the reservoir and requested it be changed. The clutch fluid should be mostly clear like your brake fluid. After the replacement my shifting feels new again.
If your clutch fluid is a dark brown color, I would recommend getting that replaced now, and spend a few dollars more for synthetic.
Your gearing oil in the rear end will break down in time at 16K you should be ok, you'll know better if you are hearing a growling or clunking sound. If you start hearing that, it's time. IMO I'd say close to 50K I would get it done.
Again using synthetics with a silence modifier in the rear end.
Same with transmission gearing oil, IMO about 50K or so. I am basing my opinions on recommended service intervals for other vehicles I have.
For real peace of mind.... Change them all out now. At the very least check your fluids for abnormal color or signs of the oil's viscosity breaking down.