I don't think anyone answered this, on a draw through you don't need a BOV.

A blow off valve is to prevent surge in the turbo as a result of rapidly closing the throttle when it's after the turbo. Think of it as letting the pressure between the turbo and throttle go. On a draw through set up this doesn't happen so you don't need it.

If I remember right F1 turbo cars had the throttle upstream of the turbo to help reduce lag. This comes at the expense of drivability.

If you want to wind up the boost using water injection to prevent knock, straight water has the biggest cooling effect (2.26MJ/kg) and it's cheap at around $1 per 1000L. A good rule of thumb is water flow should be ~70% of fuel flow. If you're using a set flow rate match it at the point where the turbo's started full boost (~3000rpm depending on the turbo).