To piggyback on RJ12's question...on an 06 GS300 Nav no ML to play audio & video from my iPhone while driving all I would need is the Vias SLVi2?

yup, sl2vi is what you need

If i have a ipod connected, can I change a song while driving from the screen if I have the vaistech system... or i need a override to that also :/?

when driving, the whole folder/file selection screen is grayed out. you can change song but only one by one using the ^ and v button. if you want to skip files or folders, you need override

I just got the PS kit and the SL2Vi-p4 in the mail. Very excited to set up the mod!

To those that have done the install for the PS and the Vais Tech in one shot, how long should it take for a DIY?

I would say an hour, maybe a little longer which is the approx time for the override install. If you've done homework and reviewed the PS instructions it's pretty straight forward once you get started. The time is spent taking apart the center console and pulling the nav unit. Plugging/installing 2 products in instead of 1 won't make much difference I don't think. I'm not a big do it yourselfer but I was able to do this and very glad I did.