How important is feeding? Will they grow faster or much faster? Will they be healthier?

Will they all die of starvation if I never feed them?

I guess so...... but you can't overfeed them either.

It's important to feed your fish, or they will die. You should monitor the Fed Meters of your fishies to see how hungry they are. If you don't feed them, their Fed Meter will turn yellow, then red, then it will go to empty, at which point they will begin to lose health from starvation.

You can also kill fish by overfeeding them, so you really need to check the meters!

whenever one of the fed meters aren't full i started to feed them and they always get sick that time i thought it's because of the environment but now i understand

I put loads of spined spotanus and stickfish in one tank and over fed them until their health turned yellow then I stopped feeding them and they were alright.