usually people top overhaul at 100k km
however before doing that, consider cheaper fixes such as engine flush/fuel system flush (and after that replace fuel filter, rm7 or something iinm lol)/carburetor cleaning first.
if it solves your problem, then you don't need to spend expensive cost for top overhauling
for gasket, replace when it is leaking, simple as that.
AC service is every 30-50k km or 1-2 years depending on your budget and/or how cold the ac is. the longer it is delayed the poorer the performance and the more work the compressor has to do (which will hasten it's deterioration) not to mention extra load on the engine. (as the compressor magnetic clutch engages more often/permanent)

for vibration, check engine mountings, and tune carb idles to suit your needs. check if the thermostat is functioning properly since you also mention that the heat goes up...
actually the car by default comes with drop in, those performance mods are typically open pods which i find not very good for our car since we can't really get a space with good CAI and our engine bay is REALLY hot especially with modded/exposed exhaust extractors

for cooling, suggest you properly diagnose your existing system/flush the radiator first

steel braided hose improves braking response and prevent hose expansion which will have spongy braking if it really gets heated up/hose expanded. it doesn't quite improves stopping power, though theoretically if you can brake faster you do brake better.

x drilled rotors that have holes aren't really for cooling, vents does most of the job which our car can't directly mod plug and play vented discs (afaik, need half cut parts and may require some mods at the knuckle)
they are mainly for more aggressive shaving of the pads (which could offer slightly better braking power) as well as removing gases that may accumulate when the pads get hot. (slots perform similar functions as well)
the cooling effect of the drilled holes are minimal.
(do google up on rotors and their characteristics such as slotted/x drilled)
if you're "not a racer", stock blanks are enough

for handling, try something like progressive springs + short stroke absorbers such as improve propex.
the rear however don't go with short strokes, and don't get too stiff of an absorber.
try to get the spring harder though

For the ac idling, consider increasing the air cond idle rpm from carburetor, and/or check on your car existing grounding conditions (if bad, replace/add more grounding cables on points such as the alternator to chassis & battery and the aircond compressor towards chassis)

for caliper modding, best if you mod the brake servo/master pump as well. only modding caliper *MAY* result in poorer braking as there isn't enough clamping force from the master brake pump

for better braking without much modding, can consider better brake pads