Nobody has mentioned the coolant, that would be second from the top on my list, brake fluid would be the top item.
Since Toyota uses a long life coolant, I would just have it drained from both the block and the radiator and refill. I would not flush.
I would flush the brakes.
I would get on the timing belt ASAP so that it doesn’t damage the engine if it breaks. Its made of rubber and rubber rots with time, not miles.
I would NOT worry about sludge or the transmission fluid. Because the low miles were put on the van via long trips, there is little stress on the oil or transmission fluid. I would change the transmission fluid somewhere between 30 to 40k miles, just a drain and refill, no flush here either.
As for the sludge. Sludge is caused by oil breaking down when subjected to excess heat. While the engine is running, the oil gets hot, but not to hot as it is constantly flowing. It gets some time to cool down when it returns to the pan. The damage occurs when the engine is shut down from hot, like at the end of a trip.
When shut down, most of the oil drains back to the pan. Some stays in the oil passages and oil filter, but a film of oil clings to surfaces like the top of the head under the valve cover. This film of oil has to absorb all the heat of the engine as it cools down. This is where most of the damage occurs.
This film is flushed away the next time the engine is started, but it contaminates the oil, making it darker and thicker. After awhile, the oil must be replaced to prevent damage to the engine. If it gets too thick, it begins to form sludge that blocks the free flow of oil back to the oil pan. Thats when real damage occurs.
Sometimes with low mileage vehicles, the miles were from a lot of short trips, which means a lot of shut downs and a lot of damage to the oil. Since you vehicle has a few long trips, the oil should not get damaged that much. The owner did do oil changes that in my opinion could have been done on longer intervals. In other words, he did more than necessary in that department.