If I get the time I'll take it apart and put up some pictures of the areas I had to mod. Mainly I had to mod the lower receiver to make the gearbox fit and the upper to fit into the lower.
Really to build a gun like this all you have to do is decide what you want the finished product to look like and then start collecting the parts for it. It took me 2.5 years to collect them, but that is because I wanted to keep cost down. I got most of my parts for free or in trades.
As far as the FPS, that all has to do with your spring, the compression in front of the piston, and what your gears can handle. I honestly couldn't tell you the exact parts in the gear box at the moment because I took parts from different guns and put them together till I got the best results. I know many of the internals are Systema, which is great since they were free, but I personally wouldn't spend the money on them new.
My first question towards helping you Patriot would be how much experience do you have with disassembling/assembling AEGs? Do you know how the components of an AEG fit together or not? If not I will try to do more detail on the take down so you can see how it all fits together.