Title re-fixed! Advance changed to Advice, you don't need a loan do ya?!
As Wa-chiss says, the S14, 1995-1998 240SX is pretty much a regular 20 year old car, nothing magical or mysterious about it. It's as reliable as any 20 year old car. Modified cars tend to loose reliability. Cars driven hard tend to wear faster. Older cars have higher mileage and aging components (materials don't last forever). Window switches stop working, control arm bushings wear out, suspension gets soft, paint peels and fades, exposed metal develops rust... all normal stuff. The 240sx is a regular car that can be taken care of by regular mechanics and has parts that can be found at regular auto parts stores. The things that make a car reliable like lower mileage, little to no modifications, regularly maintained, etc. are also the things that make a car more valuable. So, save up money, shop around, be patient and buy a reliable S14!
Your mechanical ability generally won't make the car any more or less reliable, but it can save you money. My three S14s and one S13 have all averaged about 25MPG. The S13 needed virtually no work and was super reliable. My S14s have been the same until I started modifying them, then, well, it just depends on the mods and your learning curve. There's so much experience with them nowadays that tried and true, sensible mods can still result in a reliable car.