Lexus GS 2006-11 :: Check Engine / VSC With A Bunch Of Fault Codes?

I picked up a 2007 GS350 AWD with a little under 60K miles a few weeks ago, I've been absolutely loving the car, but noticed the check engine light/check VSC came on this morning on a cold start; it also sounded a bit rough on idle. I have an Android to bluetooth OBDII scan tool for my other cars so I pulled the codes, and it's showing P0300, P1600, P1700, and P1800.

Searched the forums and nothing comes up for those specific codes. But the first couple of things that came up as culprits for check VSC were the gas cap and brake fluid; went out and bought an OEM gas cap and made sure the brake fluid was topped off this afternoon. I reset the faults and drove the car around, but the lights came back on about 15 miles later. It drives and shifts fine, but I still think it's a bit noisy at idle.

A little background on the car: The previous owner only drove it on weekends and for events here and there, hence the relatively low mileage. The car was sitting in his garage for almost a year before I bought it, he finally got rid of it because he wasn't using it. I grabbed it despite a higher asking price because of the mileage and how clean it looked, but now I'm a bit worried. Is this bad gas? Should I flush all of the fluids? MAF or other sensors? I'm a bit lost.