No temperature guage is another one. Thermostat is something else, T-valve is commonly called by public.
Pakwheelers are intended to keep car as close as much possible to factory spec. and this is some sort of battle between Pakwheelers with mentality & methodology of Typical roadside Ustaad G & Chota Shagird type mechanics
Water in radiator is not good, get it flush, treat it then fill Toyota coolant in it if there is no leakage. Also at next oil change, get your engine flushed and start using 10w40 now.
A/c sound as mentioning from your post writing seems belt but get it checked.
Your RPM is causing issue. Google Iqbal Shahid Suzuki in Karachi and get your car thoroughly checked and fixed by him.