For 1: Try cleaning the condenser and check if it gives any better result. The compressor may take more load if it gets deteriorated in condition but this will make it sound a bit strange too. Check the sound of AC compressor too. The Gas may not be refilled properly and there might be traces of impurities that may cause this. As well as local low quality AC Gas will also give you this problem (but 3S dealers do not do this usually).
Engine oil recommendation is of 10W40 grade for minerals. Anything above will get your car run a bit heavier. Try switching to synthetics, it will give better drive.
For 3: You can Flush from anywhere and can use any good branded Radiator Flush for this. Just make sure that you turn on Heater while doing this and your car should be on optimum temperature.
For Coolent, do not go for color, either choose reliable brand. Its a one time investment and does not need changes or top-ups frequently. Brands can be Fuchs, ZIC, Caltex, Liqui Moly, Toyota Branded etc.
