New to Yaris - Some Questions

[ajkochev74]

Possibly going to be getting a 2007 Yaris with 163K on it. Being bought from a reputable dealer.
Had my brother a 30+ years mechanic look over the car. It was amazing what he found, from small things like slight discoloration here and there to new or scratched bolts he could tell what had been removed or worked on recently. It had been repainted sometime recently and the driver side front fender has been replaced for cosmetic reasons. Carfax shows that the oil and service was changed at a dealership for most of its life. Going to be getting the extended warranty as well. Peace of mind for me for another 100K miles.

Anyway, what I want to know is this:

1. 5w-30 oil listed on the oil cap, Can I use Synthetic? If I don't know if regular or synthetic is in there now can I start making the move to Synthetic? Can I mix the two if I need to top off and eventually do an oil change to synthetic without harming the engine?
2. What else should I look for before taking the plunge?

Had a 97 Tercel until this year when the body was rusting out around the windshield so much I couldn't get it replaced without body work needing done. I loved that car and feel that the Yaris model evolved somewhat from the Tercel. Feeling really good about getting a Yaris so far.