Here are my answers below, im no expert but these are my views and my QT process.
1. Is the pump, sponge filter, bio-filter and carbon (might replace carbon with seachem purigen) all i need in this quarantine tank?
Yes, that will be all you need, i would not use purigen too as it might absorb medications.
2. Do i need the lights on? If yes, how long per day?
Yes, i would leave it on for 8-10 hours a day so you can observe the fish in QT.
3. I am using ReefMax Salt mix for my saltwater, do i need to add any other additives? Or should i use a different salt mix?
Fishes are not particular about salt mix nor salinity. So long it is stable, it should be fine.
4. Is it appropriate to add a rock in the tank?
You can add some rocks but i would advise not too, rocks might absorb copper and it will be harder to achieve therapeutic levels.
5. Do i need to leave the tank running even if i have no fish to quarantine yet, or only add saltwater and run the tank if there is new fish to quarantine?
You do not need to leave the tank running if you have no fish to QT, but do note that you'll need to re-cycle the tank again when you have fishes to QT again. I personally leave my QT running 24/7.
6. Do i have to do drip acclimatisation method for new fish before adding them into the quarantine tank? And another drip acclimatisation for quarantine tank to display tank?
Personally, all i do is ensure salinity and temperature matches between transfer. just mixes water bit by bit till salinity matches. Of course, be careful not to pour water from the bag into your QT, and QT into your display.
7. Is quarantine tank different for fish and corals?
Generally QT for corals should be a fishless tank that matches the parameters of your display as close to as possible. QT for corals are more difficult to maintain, i personally do not have a QT for corals.
8. Does 20% water change weekly apply to quarantine tank?
That will depend on the medication you are using. If purely just copper (or QT without medication), then yes a 20% weekly WC would benefit the system overall, remember to dose enough copper in the fresh water going into the QT.
9. What to look out for when the fish is in the quarantine tank?
Look out for white spots (ich, velvet & brook), sunken stomach, white stringy poop, etc, etc.. Just a few to name. Generally, just ensure fishes are eating well and pooping well, especially when copper is used as some fishes such as angelfish and wrasse can be sensitive to certain type of copper.