New tyres

Not sure on tread depth but the left front is better than the right front, and that's the wrong way round for Bedford.... Might have to swop them round!
 
Depends how often you do trackdays. If you're doing 1 a month then after, if it's a one off i'd wait.

After 100%

Just don't fully kill them as they'll need to be legal driving home.
 
after large tread block will move more and create more movement and heat

This will lead to excessive initial wear and wishy washy feel .

The closer to a slick the better :smile: