I have a 2002 and get between 10 and 12 L/100km in mixture of city / hwy. That's 20-23 MPG US I think.
After much online research I am convinced its non-interference but lots of people swear otherwise. I'm at 155,000 km (95,000 miles) not planning on changing my belt. (Everyone can abuse me when its breaks and strands me at the most inopportune time).
Moderately DIY friendly. Van's are not really easy to work on. But at least everything is Toyota quality.
Before I list a few trouble areas, let me say that its a great van and been very trouble free for me. Now the trouble areas: Watch out for oil sludge. Just Google "Sienna oil sludge" and you'll see what i mean. Lots of people recommend having a mechanic pull a valve cover to check for sludge before you buy. Suspension - struts don't seem to last and front lower control arm bushings had to be replaced early. Cheap plastic rear hatch handle broke twice