One of your first decisions is how much money you want to put into your "hop up." The standard engine upgrade is a better intake manifold, mild to mid range cam (something up to about 214 @ .050), headers and exhaust, and good carburetor tuning (or in your case, tuning of your EFI).
However, to get to the next stage of HP improvement you really need better heads, and sometimes your pockets are already getting empty. Machining your old heads or using better iron heads (the ones for sale always seem to be from a Corvette) always looks tempting, but it also has limitations. The best choice for the long term is newer design heads (iron or aluminum Vortec, aftermarket aluminum, etc.), but that initial pricetag is probably $800+, and that's before you start buying new rockers, pushrods, gaskets, etc. And then you start looking at roller cam conversions and other upgrades, and realize it might have been cheaper in the long run to buy a complete crate engine with all the upgrades. Isn't this hot rod stuff fun!
Bruce