Safe beginner mods:
 

I just got my 88 gxl. I love it so far. Is it safe if i just start off with mods such as a custom intake/adapter combo, custom single sided catback exhaust, used e-bay coil-overs, and ebay strutbars? Will these mods cause any problems with the motor considering the car has 165K miles?

i personally would get the motor rebuilt first specially if its your daily driver but if not a header and full open exhaust,go electronic aux port system,and suspension. but thats just me.

sounds pretty harmless, you could always get get a new air filter and replace rotten exhaust with muffler shop stuff, then you have basically no impact on the motor, just don't do anything to add more fuel yet but intake and exhaust prolly wont hurt your n/a just don''t beat on it and check/change oil frequently..

You need to make sure the car is in tip-top condition before you start modding it. Do a full tune up.

Plugs/wires, maybe coil packs, change the oil, flush the tranny, adjust the idle, do a compression check, change your fuel filter, replace vaccuum and coolant hoses, do a coolant flush, brake fluid flush, fuel injector cleaner.

That's the best starting place.

Other than that, you should be okay with a catback, I don't think it will effect the backpressure enough to prevent your aux ports from opening.

Intake is hard to do, best thing would be a cone filter and cold air box.

None of those items will cause problems, but prior to adding unnecessary items you may want to consider an engine rebuild just for reliability purposes if this is your only car. Also, most e-bay coil-overs are lousy for performance, but I guess they are OK if you just want them for looks.