The Town & Country is just the example vehicle Avis uses. It really has no bearing on what you might get. While the Town & Country has been replaced by the Pacifica, there could still be a few of them floating around in the fleet. More likely you'd get sometimes along the lines of a Dodge Caravan which are the most common minivans in the rental fleet. Other possible models include the Toyota Sienna, Ford Flex, Nissan Quest. What you get really depends on what they have on-hand when you arrive.

As for trim models, it's proabably going to be pretty basic. The car rental companies are not in the habit of ordering loaded vehicles.