I’d amend the Highlander search to 2004-2007. They have the nicer 3.3L 5AT driveline, TRACS, and other upgrades over the 2001-2003 models.
The third row is a kids row, no doubt. But only vans and van sized things have comfy third rows.
There’s no real issues with a Gen 1 Highlander. No major flaws or anything to be on the lookout for. Just history and condition. The V-6 has a timing belt so check for last change. Having a shop do a complete timing belt service isn’t terribly expensive but it’s a buying bonus if it’s done.
The rear wheel bearings usually go out 250-300K. Not hard to do, OE parts are expensive, good jobbers to be had.
Rear sway bar bushings fail at higher mileages too, cheap and easy to do.
Interior materials wear like iron.
They’re actually pretty simple vehicles with over built quality parts. The suspension is struts all around. The brakes are easy to do. Toyota used quality fasteners so servicing things usually goes easily. The only total PITA is the rear plugs on the V-6. I had my tech do them when I had the timing belt done.
Toyota indie techs are everywhere now and those older models have tons of good aftermarket parts (Aisin and Delco, etc) that are often OE suppliers.
One thing to check is the intermediate steering shaft. If the steering clunks at full left and right, it’s shot. Dorman makes a cheap jobber part that has a rep for being better than the OE one. I replaced mine with the Dorman at 150K and 220K later it’s working great. Not a hard job if you can work well under the dash.
Don’t buy a four cylinder one. The engine has some issues and the fuel economy isn’t really much better than the six anyway. The extra power of the six is very welcome. Despite being lower in power than many newer SUVs, the HL also weighs a lot less, so it actually has some punch.
