Do I need a BPV / BOV

A Bypass valve (BPV) or Blow-off valve (BOV) is not necessary with a draw through setup.

We use them with our blow through kits to prevent rotor stall when the throttle is closed. The valve vents pressure created by the blower to atmosphere when the throttle is shut - Similar to the way that a BOV works on a turbo. If you want to use a recirculating type - you run the vent to the airbox so that you do not waste that already filtered air

A true blower bypass is generally a gated valve the reroutes the entire intake flow to bypass the blower. Generally they are an integrated part of the blower - as in the case of OEM Eatons used on production Chevs and Pontiacs, and have a large integrated gate valve controlled by an external actuator. They are often coupled with electromagnetic clutches to completely disable the blower

When running a Bypass on the blow-through system, the valve flow volume has to exceed the output of the blower by a safe margin. On a turbo if the BOV doesn't outflow the turbo it will just slow and eventually stall. But because a blower is directly coupled to the engine, stalling it creates a pressure spike in the intake, That rising pressure will find the easiest path to freedom (wherever that may be). 

Turbo BOVs will often not flow enough to be used with a supercharger. You will also find that the spring rate in a turbo BOV is often too stiff for use in a supercharger application. The valve we use flows 330cfm. The AMR will flow approx 150cfm.