Rough Idling and Engine overheating during long drives

I just bought A 2nd hand Mazda 323 Familia Sedan model 2000. At first had no trouble cold starting then later on It had a problem of cold starting that I need to warm it up at least 10 min. before I could use it without stalling. I t has a hard time going uphills, and stalled during steep climbs. Then recently, we used it for a long drive to Pangasinan with 5 passengers and at least 25 kgs of baggage. Then halfway NLEX the temp. climb and stopped over a service station to “cool” the radiator. When i opened the radiator, there was no visible coolant on the tubes and added coolant. The coolant reservior was “full” and there was no visible leaks in the system, and noticed the area near the reservior was wet with coolant. This is with the AC on, and later turned it off the rest of the way to reduce load on the engine. I presume the engine was overloaded that caused the overheat, and maybe the cooling system needs to be cleaned or serviced.

when I got home, I replaced the ignition coil to somehow remedy the “weak power” when going uphills and accelerating. When i finished replacement, I tried it, and solved the cold starting. But the engine idle went up. i tried adjusting carburator idler but it was already minimum. Next i tried the Air/Fuel ratio screw (i think) and the idling went down a bit to a point the engine begins to rough idle and “knock”. Still I think it was still idling fast.

What suggestions do you have to further lower the Idling?