Wastegate=Turbo.
The only way to alter boost on superchargers is pulley swap.
You can use a blow-off valve. .
No, A BOV will dump ALL Boost, you need a wastegate, Yes the WG needs to be Pre-MAF
...if you use an electronic boost waste gate controller you can not only select the psi you want you can custom tailor boost versus rpm. If power drops off after say 4500 rpm you can add more boost (and tune for all this) at/above those speeds to elevate the torque and the resultant horsepower.