Intake manifold/ general mod advice

My advice would be to research what heads and possibly cam would compliment that intake, just the intake alone will likely just make your horse into a dog with stock heads.
JMO, I sure others will chime in.

IMHO, no at this time you don't need that intake. If you are planning better heads down the road you can certainly run it, but that intake, and the 75mm TB are a bit "big" for a stock head/cam car.

If you were planning on keeping the car relatively stock for the foreseeable future, I would recommend an early (with the EGR) explorer intake manifold and early explorer 65mm TB. You can usually get that all for under $200 and it will be a nice match for the stock heads/cam.

Now, if you told me a year from now you were planning an Aluminum headed 331 with a radical cam, i'd change my answer. Really it's your call as to where you realistically see yourself going with future plans, and how to prep for it.