Buying on door will suffice.
Parking could be 5, if syou show up on thursday, chances are you pay nothing.
Places to watch? Radillion, even has a bar. Kemmel/Les Combes, La Source. Busstop isn't what it supposed to after the big change.
Crossings will show themselves when you're wondering around. A walk around the circuit is doable during the race.
Signing session? whut?
Grandstands are free accesible.
Be prepared for any kind of weather. Looks like it will be raining thursday/friday, with clouds on saturday.