Sounds just like my first Punto
Model: I think the easiest way to check if the car is a facelift model or not is to see if it has body coloured bumpers - ones without are pre-facelift & ones with are facelifted! The SX model is kinda mid range model, the 75 SX came with either 3 or 5 doors.
Equipment: SX models come with drivers seat height adjustment (be careful when raising the seat as the handle was quite flimsy on mine). It also has lumbar adjustment, steering wheel height adjustment, central locking (not remote tho, thats on ELX models), elec front windows, sunroof (not electric), front fog lights, digital clock up by the sunroof, rev counter & temp gauge (doesnt sound exciting but the lower models didnt have these!). The 75 models specifically might also have steering wheel mounted stereo controls for the radio casette.
What to look for: The only thing that wore out / went wrong on my Mk1 was the rear radius arms. They can be spotted by a knocking noise from the back of the car when moving, but they go gradually & not all of a sudden. mine knocked for about 3000 miles & i saved up to get them replaced. They cost me £150 to be done at a Fiat dealer. The head gaskets can go on 1.2 8 valve Puntos particularly, tho i think the 75 is less vulnerable to this than the 55 & 60 models. Either way, check the oil filler cap & coolant cap for mayonaise like white stuff. Also, the temp gauge should usually sit between 1/4 and 1/2 way when driving, once stationary, on my mk1 & another couple ive driven, it's risen to just under half way and then the fan came on to cool things down. Another thing i used to notice is that my Mk1 didnt like being rushed when starting up. I used to turn the ignition on, a pump would start & an icon that looked like a shower head wud light up below the rev counter, when the pump stopped & the light went out, id start it up. If i started it before this point it wud sometimes turn over for longer & sometimes the CODE imobilisor light wud stay on, so i just decided to give it chance to do it's stuff & it was happy as larry, didnt have a wink of bother in 18 months & 25,000 miles.
Hope that helps!