I don't mind the platys breeding too much. A majority of the fry that are born become food. Those that survive do well. It's like a natural selection and works well in my tank. If you have places for them to hide, some will survive. If you don't they will all get eaten. I think I have a good balance although all of the natural rock is currently out from the move. I need to get it back in soon. The black skirted Tetras have done a good job at keeping the baby platy population down. There are 2 types of baby platys, the fast ones and food!
Live plants are nice, but you have to watch your lighting or you could end up with algae growth. Even worse, you get a live plant that has snail eggs on it and you will have a battle to get rid of them. My friend had a snail infestation that took 2 months to get rid of! The other thing you have to watch with plants is some fish will eat the plants too.
I use an air stone to oxygenate the water and it works fine. I have the long flexible kind, so I like to crank up the air during the day for a wall of bubbles across the back and lessen it at night. It's hidden under the gravel, so it's a cool effect.
They are very self sustaining once set up too. I clean my filter, run a gravel vac and do a 10% water change once every 2-3 weeks and the water is crystal clear. The right filtration will make a bg difference with that though. I use the 4x rule for filters. The formulae is you take the volume of the tank and multiply that by 4 and that should be the volume in gallons/hour flow rate for the filter. Some recommend 2x, which does work okay as well, but tanks cleanings need to be very regular, or you get algae, even with Plecos.
So for my original 80 gallon tank (80 x 4=320), I got a 320 gallon/hour filter. So essentially, the water in the tank is filtered 4 times per hour. I use that filter now on a 46 gallon tank, so the water stays very clean.
One very important thing that some forget is to make sure you wash your hands before feeding the fish or putting your hands in the tank. Clean hands=healthy tank.