Your car already has a diaphragm-type bypass valve installed. You'll always need a valve of some sort. Many people on these boards like to relocate the MAF to the cold charge pipe so they can have their VTA "pssssh" sound. It isn't necessary to do this and is purely for aesthetics. Our MAF sensor was designed as a draw-through type and being as it's a $250+ part I'm reluctant to do anything to it that might shorten its lifespan in any way.
Personally, I went with the Forge bypass valve that they make for the Mazdaspeed Miata. It's a piston-type valve which is much better than the RX-7 valve that Mazda included with the car. It's 100% serviceable with just some high-temperature grease. I used two 45 degree silicone hoses to make it work. Coupled with the Turbohoses SRI the sound of the bypass valve when I push in the clutch is loud and noticeable.
The stock wastegate actuator is adjustable and s probaby set to about 6-8psi if it hasn't been touched. It's also a well-known point of failure on our cars. Mine went out a couple years ago and I replaced it with the ATP non-adjustable actuator (it's set around 7psi) since I already hit fuel cut on colder days with my bolt ons.
10-12psi on stock internals won't last very long, even with engine mangement. Stock connecting rods are weak weak weak. Save your money, build your motor, then turn up the boost. In the meantime, refresh or upgrade your brakes and suspension. I promise you'll be braking or turning far more than accellerating in a straight line. Your car is going on 13 years old and would probably appreciate some TLC there.
Good luck.
