Sounds like a model 29B, the model I have as a 2004 Itasca Spirit. Eleven years, 32,000 miles experience, picked it up a year old with 4000 miles on it.
The floor plan is useful for a couple, usable by four or five adults, the dinette sleeps children only. With two slideouts it is relatively heavy for the Gross Vehicle Weight Rating of the chassis, and with a short wheelbase and long rear overhang, weight distribution has to be watched carefully to keep it from getting light on the front end. Not carrying extra people, I load my heaviest stuff in the forward bins and drive with the fresh water tanks (forward of door) full and waste tanks (behind rear axle) as empty as possible.
The short wheelbase means a tighter turning circle, but it also means that long rear end swings out pretty far; in 11 years I've tagged something with a rear corner twice, first two years of maneuvering in tight places. On the plus side, if I can back into parking spaces at the edge of a lot and put the overhang off the lot, it will fit into a space that works for a crew cab dually pickup.
For condition of the house, you need to make sure caulking of seams and openings has been maintained, so that it hasn't leaked or the fiberglass roof has not separated from the channel at the top of the sidewall. It came with slideout awnings, the original equipment awning material was know to deteriorate quickly exposed to sunlight, mine lasted about five years before peeling. A&E replaced some of these under a warranty extension.
The only significant chassis problem has been brake calipers. If not driven all the time, you can expect one or more OEM calipers to corrode during storage so that a brake won't fully release. Later model years of E-450 got a better caliper, these are used as replacements for the earlier ones. I replaced mine at six years old. Another cause of brakes sticking can be collapse of the rubber brake line to the caliper, these also have better replacement parts.
I've averaged 8.2 MPG over 32,000 miles running mid-America speed limits. You might expect to see as low as 6 MPG and as high as 11 MPG on individual fillups, depending mostly on cruising speed and interaction with winds (which are a big thing out here on the plains, 70 MPH into a 20 MPH headwind is like trying to run 90 MPH).