Downsview is my go-to TTC station when I need to stay downtown later than usual and don't want to take the GO bus at night. Parking is available for a $4 fee if you arrive in the morning and half the price if you arrive in the afternoon. It gets full pretty quickly. Just this past Monday, the parking lot was full around 8:20am whereas in the past I was able to find parking even around 8:40am.
There are 2 entrances to the underground station. One is at the entrance by the passenger pickup and drop-off and the other is by the bus terminal. When you're leaving the station, choose the correct exit because they entrances/exits are not connected.
Since it's a terminal station, you will always find a seat on the train. Don't be surprised if there are passengers who ride from Wilson station to here just to get a seat :) There is currently no wifi at the station, but it's arriving soon. The station has washrooms that are clean.