During the spring, summer, and fall it can get very busy. If you go early in the morning or late in the afternoon or early evening you should be able to find parking. There are several parking lots located in different spots around the arboretum. Weekends this time of year are the busiest.

Leash only on trails, not allowed in certain areas like the Japanese Garden

yes i take my dog walking there on a leash and with poop bags... its very relaxing and beautiful in the fall.

Yes, it's a little small and narrow for biking. Mostly walking. It's nice out north toward the water.

Yes. You can ride a bike on all paved surfaces which run throughout the park.

Yes, by bus. Check King County Metro bus schedule on line,

Yes you can visit later in the day.

There's a very limited amount of parking inside the park. The largest lot is at the Japanese Tea Garden. There's another one over by the info center. The last "big" one is just north of the info center but may be closed off due to construction in the area (6/2016). A couple of small (5-20 vehicles) lots are just off the main road, one near the overpass and another closer to the tea garden. Otherwise you can find parking near the south entrance on E. Madison or in the residential areas just to the west. Arriving early makes finding a spot easier.

In agreement with the other postings about the length of time. As a photographer I would likely take at least 2 hours stopping to take pictures. If you are planning on seeing the Japanese Garden, then add more time in. I actually have gone to the Japanese Garden separately from the arboretum. If you get the opportunity to do the tea ceremony, I highly recommend it. It is very much a part of my culture and it reminds us to slow down.