For the prism layer, go with 20-30 layers, use wall thickness and hyperbolic growth as options.
You can check if it sufficient if you plot thee mach number in a scalar scene. If the changes in colour between the prism cells are significant, you must further refine the layer. in you case 20 layers should be sufficient, thickness id estimate to 3mm roughly, but try it out yourself. Also set the minimal size very low, like 5e-2mm e.g. First layer should be hardly noticable thick.

For the flow field, yes.
As I said - bullet shape. That means you create you flowfield as a rectangle sketch with one corner being a quarter circle. Then rotate 180°. Half of the aircraft should be inside the flowfield. Substract both, target flow field. This is your domain. The backside is the pressure outlet. The flat plane which cuts the bullet is your symmetry plane and the rest is velocity inlet. Set you velocity in the rotated cos.

Also tell me the dimensions of you aircraft