i heard you have to buy insurence sepertly for that track and there seem to be a corner located under a bridge 
No, no separate insurance

Actually the track is from the french Government. The french Police-motards come and practice with their bikes for improving their skills. That's why the track is open from 14.00 trough 18.00 hr (O8.OO till noon it's open for cops).
Wednesday is kids day, so no riding on Wednesday.
The bridge is situated right before a 180°degree corner taken in first or second gear.
Tires can be found in (i believe) 3 shops in Lille. Since that town isn't so big it should be easy to find.
Official Belgian price for a rear Mich Power is 244 €, so you'll pay like 125 for a rear, without the work which is another 10 to 13 €