That price sounds high, but depends on mileage. It's about the retail for a really nice one. Go to www.edmunds.com and get the true market value for your area. Remember that when the 2005 models come in, the 2001 prices will drop.
Insurance depends mostly on your area and your age. It can range from $800 to more than $2000 per year, depending.
As for hoods and other mods, you should probably wait till you get your car, then select a mod theme, and make a plan as to what to do first.
The IS300 uses premium grade (at least 91 octane) gas.