There are Dallara manuals available, although not sure if I have one for the 95/6. There is one for the previous and subsequent models, and I doubt much changed that's important at our level -
http://nordicf3masters.eu/lang/en/fo...itors-2/manual
Seat belts will need replacing for racing, but for testing you may be okay if the belts are clean and tidy.
Fire extinguisher needs to have pressure to be legal in the UK. Getting it serviced/refilled/rearmed may be difficult if the bottle is more than 10 years old or thereabouts.
Spares are findable, depending on whether you are rich or not. Dermot Healy has a few bits and bobs for these cars most of the time. There are people around that can make suspension, suppliers that can get wings... Depends what you want/need.
These cars are pretty solid really, so you shouldn't need to replace too much unless it's been poorly cared for or damaged. Just a case of going through it methodically, making sure the wheels won't fall off, the brakes work (and release), and that the engine/wiring/coolant/oil is behaving itself...