The trail is mainly crushed gravel, with some paved portions. It is designed for single file travel. Trikes and bicycles can pass easily in most portions. It would be a tight squeeze (but possible) for trikes to pass one another.
The route we rode through the park ended up being just shy of 10 miles long. There are views of Green Bay (the body of water, not the city), however most of the trail is through a forest canopy. Stops can be made throughout the route at restrooms in the park.
Peninsula State Park can be very busy and the trail crowded. I'd recommend riding in the morning on a weekday to try to avoid the crowds. This is a nice trail, however there are other routes in Door County that offer paved roads with less congestion and traffic.
Make sure to stop by the park entrance headquarters and pick up a park map. The map details the Sunset Trail, roads and other attractions within the park. Note: if you need a sink with running water and flushable toilets, go inside the headquarters building!