How do I choose the correct params?
A flying wing needs an airfoil with an s-bend, so no regular airfoil (none of the ones you mentioned). And you need to incorporate a significant twist towards the wing tips to make it fly stable (incidence is about 10° lower at the tip).

Knowing your turn radius and your desired speed your bank angle is a given, independent of aircraft mass. You can compute it with the centrifugal force and the lift portion that points into the turn... 

r = TAS * TAS / ( g * sin( bank ) ), with true airspeed (TAS) in m/s, g = 9.81 m/s/s, r in meters. (if I'm not mistaken)

When you know the mass of the aircraft (roughly) and your airfoil lift coefficient that you want to work with (e.g. 0.5 to 0.8 or so) you can work out how much wing area you'll need to fly that turn without stalling. You could also chose a wing loading and compute the lift coefficient for your turn using the basic lift equations and the force equilibrium...

25 degrees is a good bank angle for passenger aircraft, more makes the passengers scared :) Not applicable here.

I'd start with an existing design of a flying wing and then make alterations to that. A famous aircraft that comes to mind is the Horten H.IV glider. Another example could be the Marske Pioneer 3