Leatherlip

I just bought a 2010 GS350 AWD and it has stock 17" rims. Tires are going to need replacing in a few months so I want to determine if I want to change rims as well. I don't want to lower the car or change suspension in any way.
I do like the look of the larger rims.

So, here's some wheel-newbie questions that I home I can get some opinions on.
1) Can I put 18" rims on, if so is there anything I need to watch out for (sizing, matching of tires, etc)?
2) I see some 19/20" wheels on many of the cars here, can I put 19" on a GS350? (I wouldn't likely want to go any larger). If so, anything to watch out for (sizing/matching of tires, etc. etc)
3) Assuming I'm looking for an upgrade to the style, but not really needing any performance enhancement, are there best choices in rim size as well as tire size? (Will some cost more than others due to how common they are)?
4) Is there anything else I should think about when considering a rim change?

Thanks to all!

msgs350

iTrader: (2)

Stick with 18x8 with offsets around +40 and make sure it clears the brake calipers. Match the tires all around, get 245/40/18 in a decent brand.

ibidu1

iTrader: (1)

I have a set of sumitimo tires for the 17" for sale if your interested, im in Tampa