Lights

Can I ask a few questions so I know I'm doing the right thing?

How long should I have the lights on for every day?

How often should I feed the fish at the mo and should it be different when the fish have all settled down and are not sick

Am I right that when the tank is ok I should change water - about 30% every week?

Any other things I should be doing?

I have my lights on for around 8 hrs a day, i'd feed a very small amount every other day. Fish can have all sorts of problems with over feeding & the water quality will deteriorate much quicker with excess poop or uneaten food.
Maybe a treat of boolworm, brineshrimp, veggies etc once a week instead of flake to give a bit of variety.
A water change of 30% weekly sounds fine. Once everything has settled down and the readings are at 0-0 for ammonia & nitrIte, test the water weekly to give you an idea of what is going on

Lights dont matter unless you have real plants. Feeding - at the mo, while you have water quality problems I would keep to a minumum, say 2 or 3 times a week and then just as much as they can eat in 2 minutes. Dont worry they wont starve!

Water changes of 30% are the minimum I would say - I change nearly 50% each week, as well as a gravel vac to keep the level of muck in the tank down.

jammy, I cycled the tank with fish (BIG mistake). I think I fed the fish every three days or so while the tank was cycling.

When the cycle was complete and I was sure the tank was stable then I fed them a bit more often - every day, but just a small pinch, not too much.