Let me see if i can shine some light on helping you mate
You are looking at getting a spyder imagine marker (good choice for a starter)
first when you get the gunmake sure you adjust the trigger so that it is sitting just proud of the micro switch....makes shooting a lot quicker.
When you get the marker...get a viewloader 12volt revoltion loader (or revi for short). Make sure it has an x-board fitted (thats the electric circuit board that runs the controls on the hopper). This will help you get more paint thru the marker and hence fire faster.
You do not need a smoke stack, load extension or anything like that, trust me....i can do about 7 balls a second at full tilt (and no aim) with my imagine and i have only choppped one ball in over 14,000. (i do recommend getting a spare feed tube though (about £3/$5)
Get a new barrel, i recommend a DYE Xcel. its a good cheap barrel and a massive improvemnt over the stock one. Which ever barrel you get will be a big improvement....after that it is just how much you want to spend. (i have seen people using freaks, J&J, DYE and Smartparts barrels, they are all about the same...just some are 3 times the price than others)
Make sure your CO2 bottle has an anti-sypthon tube fitted
From there my friend....go out and get used to the gun. Dont spend millions on a gun that you may not even like the feel.
Once you are used to how it feels...then start buying all the flash coloured bits, the turbo this and the rolls royce that.
Have fun and enjoy.
Hope this helps mate