Being over the 400 mark myself, allow me to try and help you.
My suggestions are based on your desire to get a cam. Get the vehicle up to par or better on all maintenance items. struts, shocks, brakes etc. Then beef up the transmission, power must be transmitted.
From there ask millions of questions on many forums and learn about the various mods and decide which would be good for you. I've found and installed many S1X and XP cams, they are relatively equal in the way they will both max out a stock set of heads and perform.
PCM wise you will require the P0300 code to be removed as both cams set the multilple misfire P0300 code. Beyond that a good tune is in order. You can run on the stock programming, you can run on a canned off the shelf tune from a vendor, but the best tune and power comes from a custom tune that was done on your car, for your car. This requires hours of tuning and yields the best results.
At this point, the only thing I haven't replaced, rebuilt or touched on a car is the connecting rod bearings and main bearings. If someone goes that far they should have a machine shop line bore or check all pistons etc..then at that point the cost to have them assemble would be low in comparison to the rest of the machine work.
For someone to give you an HP gain per part is tough as each car behaves a little differently. Typically the first pulley drop gives you about 20hp and after that it'* 5-10hp per drop. Exhaust merely allows better flow which in turn will give the motor the ability to create more power. I notice you mention flowmaster 40'*, I'm still on the stock muffler and finally am starting to max out the flow. It took a bit though.
Gen V SC with 2.9" pulley
Northstar TB with 4" FWI
Learning the mods you want and where you'd like to be is the first step. Step #2 is money.
Ripping the tires free on dry pavement from 35-40mph and going up in smoke is an amazing feeling though.