Put in the budget a new engine, and repairs. I have not been around here very long but I have been around enough cars and shops to know from previous experiences. I cringed when I read your post. I've seen enough of them, I'm going to throw all these fancy parts on my car and run XX.XX No real understanding how they work w/ each other.
Before you start modding take a good hard look at the car. Do a compression test, oil change, put the oil that came out of it through a slow strainer, look for bearing material, metalic, any thing and everything that does not belong there. If possible drop the pan and look at the pan and strainer, dents in the oil pan should be pounded out, junk removed. Look at your bottom end, does it look clean, or nasty? If you have the tools, pull a bearing cap and plastigauge. That will tell you alot. Drop the down pipe and IC pipe, check for excessive oil. Blades on turbo, shaft play. Turbo's are finicky, they don't like to be pushed. A turbo desingened for 7 pounds won't like trying to make 16 pounds for very long. Then go through the engine bay, anything that does not look stock, pay attention too. Figure out what and why the p.o. did that.
I worked as a factory dealer tech for a couple years and a shop for a year and a half. In that small time I have seen alot of stuff. From waste gates hooked up back wards or not hooked up at all, to some seriously evil home brew setups. Some good, some bad
Sorry for the long post and I am not trying to lecture or come off as a internet know it all, but my advice is sound. You say the previous owner did this and that, so now it is time to find out what he really did. I.E damage and or wear. Plus you are dealing w/ 18 yr old parts
Me and others have seen it countless times, kid spends 10 grand in upgrades, motor blows a week later, no money for repairs, car gets parted out for half of the price, so he can try and buy another car