It's time that I need to book my second service for the G, am I ok with simply getting the oil changed or do I need to have a full check up done?

The tires don't need rotating and I really doubt there has been significant wear on the brakes or other systems at this point.

Will there be any impact on my warranty if I go with the schedule 2 service that is just an oil change and leave the check up for the 24k service?

 

Of course you go with just the oil change unless you have tons money to burn. But if that were the case, you probably wouldn't have bought a lowly Infiniti. =)

And no, there can be no possible impact on the warranty since you are following a recommended maintenance schedule. Also, all maintenance should be documented.