no you need to add water conditioner to remove chlorine and other chemicals from the tap water or else the fish will die. and it would probably be better to let it wait longer to put the fish in so you can let some bacteria grow. without it your water quality (ammonia, nitrite, etc.) can be stressful for the fish.
Shutting off the valve doesn't drain anything. You need to open something lower than the faucet and open that faucet to let air take the place of the water.
Its ok as long as you let the water cool to room temperature before adding the water back to the bowl, or adding the betta to the water. Also, it is completely unnesseary to boil before putting in your betta's bowl.
nothing
Take the battery out and let it dry out overnight.
It is too low if it is below 24 or even 26 degrees celsius. A thermometer will let you know if it is in too cold for your betta.
Turn main water supply off in your basement. Adjust or replace shower shut off knob.
It depends on the faucet but generally it would be a screw or lever.
Sometimes a leaky or broken bath faucet is too difficult to handle on your own and you must leave it to an expert. It can take a while for a plumber to get to your house to repair a bath faucet, so while you are waiting to have it repaired, don't let all that leaking water go to waste! Place a bucket or large bowl under the faucet and use this water to water plants or to soak dishes in before you wash them. This is a great way to conserve water, too!
let it flare to a mirror or another betta fish 24/7 for 3 days feed freeze dried blood worms or frozen clean water do a quick fight with your betta with another one 1-3 minutes
The volume of water that comes out of the tub faucet is much greater than the volume of water that comes out of the kitchen faucet. Let's say that the bathroom is twice as far from the water heater than the kitchen, so twice as much water has to be run to get the hot water. If the tub faucet allows more than twice as much water to pass through, then it will get there faster.
maybe if you have a warm house. but if you plan on breeding Betta fish in under 70 degree water, let alone housing them, your betta fish will probably die.
Assuming that you tuned the faucet to hot and let it run until the hot water should have reached it, you may want to check your water heater and make sure that it is working.