I like your idea but I'd either go 1 year newer for the ease of maintenance or 10 years older, same reason, ease of maintenance.
I'd look at the 2017 to 2020 Sienna with the newer 3.5 as YouTube's Car Care Nut says easier to work on, the earlier 3.5 just doesn't have much room, 2010 Sienna being my experience here, though they are fairly reliable if the one time something does need repair and the motor has to come out, resources better be there, whether it's cash for a shop or ability to do it yourself. I think you could still get the certified preowned warranty with one of these 2017 and newer and with the over-all cost I'd want the warranty, but this is way out of my budget for a vehicle and I am only here to voice an opinion of what I'd look at.
In this specific instance I think the 2004 - 2006 Sienna and a budget of $4 to 6k, the location should have a few limited rust examples available and the "Maintenance Technician by trade" should be able to work through service work, timing belt, coolant plate re-seal, center sliding door hinge; though there still could be be a drip coming from behind the flywheel which is either main seal and/or oil galley plug, just add oil until transmission has to be removed. And keep the other cars as necessary.
Not going to knock the other choices but to say watch Kia 3.3 and the head bolt issue as it evolves and Honda would be my second choice for something that was less than 5 years old and biggest warranty available. I think like up to 2003 -07 Dodge with around 100k if I went that route being I heard good things but no experience to say much more. I didn't read page 2 - 5 so excuse me as I may be light on some comments.