You do not really need the cichlid stones, my BN pleco spend more time in them than my cichlids do. As long as you have a decent amount of rocks, the fish will be happy. You can get dry reef rocks (macro rocks) and they will be cheaper long term.
If you are getting the HOB filter (look at Penquin 350B or 400), then you can get away with not having the air pump / stone as well, the waterfall effect from the HOB will be all you need for gas exchange / oxygenation.
If you want to do a natural look of Lake Malawi there are very few plants in the lake, however, they can provide additional hiding spots for fish / fry should you wish to use them. You can also look into real plants such as Java Fern and the larger Anubias, both are cichlid friendly, they will chew at them a bit but not as much as some other real plants, they are also beneficial as they will help export ammonia, nitrite and nitrates from your tank.
Perhaps instead of 1 300w heater, look at getting 2 x 150w heaters and put them at opposite ends of the tank, this way in case one ever dies (which does happen), then you have a backup, whereas with just one, if that dies, the tank can quickly get too cold for the fish.
In regards to the test kit, API MASTER kit is highly recommend. There are some additional things you would need to know about the Nitrate test should you decide to purchase this kit. It is highly recommended to stay AWAY from the test strips!, they are very inaccurate.
Hope this helps.