You know you own a true mazda when the side mirror doesn't work. If it works, you got sold a lemon!

Just kidding. Either leave it or get it fixed outside, it would be $250+ including labor. FL fixers can doit cheaper, or quick fix is WD40 spray inside.
Yours is power seat I presume? It is normal I guess, how does it feel clunky? I don't find my ex Maz3 power seats smooth, a bit of jerks.
Engine is always loud on cold start, it roars then after a while goes down and stops shuddering heavily also.
For temperature light, just drive normally, once the car starts, the old school me will wait until the RPM drops below 1K before engaging D, then in about 100m, the temp should reach the end of the blue bar, then I on my AC, but sometimes too hot, I just on the AC direct. The 1K RPM is a must for me.
Roads in SG typically,
TYPICALLY is slanted fo rthe purpose of draining rain water. It's not obvious, but it is actually. I'm not sure how bad it is for you.
Check your AC coolant with a workshop and top up. My Maz3 AC is cooler than most toyota and my sister's honda.
Capacitor is not that ex... you can get it done at HALF the price outside, the issue here is you went back to TEK for servicing and checks.
You can try outside workshops like JDM, Monster Garage or my personal favourite - Autosaver for repairs and fixes. They get it done at a fraction of TEK's cost and wayyyyyyyyyyyyyyy faster than TEK.
Toyotas are quite maintenance free, especially the older models as they don't have that many ECUs compared to the newer cars. Maz3 deluxe alone has quite a fair bit of electronics to worry about.
So if you want a gimicky car, but don't want the repair cost and issues, a bit hard... it's like buying a Conti and expecting it to be easy to maintain and fix like a bicycle.