The early 2003 V6 had a fuel rail recall, other than that it should be a good engine. It hasn't been around as long as the V8, so the long term durability/reliability is unknown. However, Toyota has a lot of faith in the V6 design as it's used in almost all their V6 applications. Tacoma, FJ Cruiser and Tundra's use this exact engine. Lexus GS300/350, IS250/350, ES350, RX350, Toyota Avalon, Camry and Sienna all use a variation that's derived from the 4.0 V6.
More info on the GR engine family.
Rattles, there aren't many other than the squeak from the right rear seat and possibly front seats.
I have a V6 and I'm getting about 18mpg mixed city and freeway. The real difference between members here with the V6 and V8 is about a mile or two per gallon. 2WD will get a tad more mpg. Do a search for mpg and there are many threads on the topic.
Good luck.