Buy all single brand for reference trouble shooting in the event of a fault.

Personally, I dont feel the different coldness between 1hp and 1.5hp.

For living hall, depending on layout, you can install 2 units 1hp at different location for faster cooling instead of one 2hp.

3 phase power supply ?

Yes.

I run 2 units 1hp and 1 unit 2hp every night. Try not to on every unit at the same time.

Good enough, 3x 1.5hp only consume 18A load typically (for all three)

The biggest appliance apart from hob/built in oven will be your water heater.. one WH (3600W) already use 15.6A by itself

If its a new house likely to have single phase 63A incoming TNB.. more than enough

If its older place.. last time incomer only 40A so a lot of people use three phase (3x 40A = 120A) as aircon then no inverter (high inrush current when start from 0)

My landlord in apartment refused to install aircon in the living room which gets very hot due to facing setting sun. But has no objections if I'm to install it. Yeah he thinks I'll just leave It when I leave.

To not give him the pleasure, what 1.5HP aircon is easy to install and uninstall later on? I'm thinking of puttingbthe compressor on the balcony since its not used anyway..

Got few Sharp at my partner's house..their AC use about ten yrs plus no problem with the AC. Only now start dripping water coz the drain pipe clogged, but AC still operate fine. The product OK wan, just the installer route is questionable, make drain pipe as vertical as possible and horizontal need slope (dont make too flat, water ponding = grow algae = jelly clog up)
Nice to haves but if old one nothing wrong no need to change IMO.

Anyone extends warranty for air cond? Am going to install Daikin inverter series in condo, is it worthy to extend another 3 years (RM205 for 1.0HP; RM219 for 1.5HP) as advised by salesperson? According to him, Daikin has 35% of becoming faulty zzz.

Generally, better known brands will less likely to fail and that is one reason why it cost more than lesser known brands unless one is unlucky to receive a lemon unit.

Extended warranty by retailers are normally insurance based coverage and all claims are subject to waiting period pending approval similar to a vehicle claim.

If you are looking for extended warranty  I suggest you buy a brand that is directly provided by the manufacturer. If at all there is a fault, repairs or replacement will be provided with no questions.

Is not feasible to buy extended warranty for a product which is of low value where repair cost is 30 to 50% of a new set.
I have been using Pana non invertor for many many years and have a total of 15 units. Is a good choice for me. No major issues other than 1 lemon unit received.

I've never bought extended warranty especially with Sharp brand
Then you'll probably choose which one has higher efficiency thus saving you some $$ long run

Nope. More like upselling because that 200 sth can replace almost everything in terms of parts..except compressor which usually warranted for 5/7/10 yrs..
If you gonna use it frequently ie everyday, a NON is cheaper by 2 or 3 hundred but the increase in TNB bill at 0.518 per unit gonna add up prettt fast that it makes more sense to get inverter.

Reliability of any appliances mainly depends on the user.

For my current place, the non invertor ACs are used daily and 80% are more than 10 years.

Temperature are set between 23 to 25 depending on weather. Filters are cleaned every 3 months. General diy cleaning yearly and major every 2 years.

Finally, you need the correct hp, otherwise, the best brand or tech will also fail.

Generally a NON's compressor will be harsher use than an INV and thus the wty period of compressor motor also reflect that  Assuming no hardware failure, the usual cause of AC failure after ten plus yrs would be the electronics failing due to capacitor leak or aging (old age electronic failure)