Welcome to FishLore! I think Isabella has you on the right track! In addition to what she's already stated, here's my 2 cents:
1. Undergravel filters are considered obsolete by most hobbyists these days because they suck all your nasties down underneath the gravel, but they are never removed out of the tank. If you have a power failure, you run the risk of all that stuff seeping back into your tank and hurting your fish. You also will probably not be able to grow many plants with that kind of system because all the stuff the plants need will be sucked away from the roots. What you can do with an undergravel filter to make it more up to date, is to reverse the flow so that it pushes the flow up into the water table and your hang on back (HOB) filters can then catch the waste.
2. You say you have ammonia in both tanks already. Do you already have fish in the 50 gallon, and if so, what fish are they?
3. In a larger tank, Isabella is right, that 2 heaters are better so you don't have hot and cold spots in the tank. Plus in a heater failure, the other one can take up the slack hopefully until you can get a replacement. I recommend stainless steel or titanium heaters. They don't break and the ones I have (ViaAqua) have temperature controllers that are outside of the tank so you don't have to keep dipping your hands into the tank to adjust the temperature.
4. Do not use the fish store water! If that fish with ick is a new fish, chances are, that's where the ick came from. Please do not add any more fish until your tank is cycled! When we get a list of the fish you already have, then we can help you treat the sick fish.
5. You should always stock your tank with the adult size of the fish in mind. Plans to upgrade to a bigger tank later on don't always happen, and you end up with an overstocked tank and unhealthy fish. I know the tank will look pretty puny when the fish are babies, but your tank will be much more enjoyable and the envy of all your friends if you know how to stock it properly from the beginning. We have profiles here on FishLore that can help you with your choice of fish.
http://www.fishlore.com/TropicalFishProfiles.htm
When I first started in the hobby, I spent hours on a website that sold fish, but it also listed compatibility and tank requirements. It's still a good place to learn about different kinds of fish, and I go back there sometimes:
http://www.liveaquaria.com/product/categ.cfm?pcatid=830
Having said all that, I think you need to start from scratch on your fish selection. Pick your most wanted type of fish first. For example, if angels are the most important fish for the tank, decide what kind of angels and go from there. Only get 2 though. The 3rd angel will be bullied especially if you have a breeding pair. I would skip getting the bala shark. They can grow up to 18 inches long, which would be too big for a 50 gallon tank. The red tailed shark would probably be fine. The kissing gouramis would be fine if you didn't have the angels in the tank also. I don't think they would get a long very well. I would wait on the discus also. Discus really need to be in groups. They are expensive, quite skiddish, and their water requirements are much more demanding than other fish. You will be doing a lot of water changes for a discus tank if you want healthy discus. They are so beautiful, but they are also high maintenance. Not a good fish for a rookie, but something to look forward to in the future once you get the hang of things. Ammonia at any level in your tank could kill your discus easily. I'm not sure about the upside down catfish. Depending on what other fish you will have, they might be fine. They are pretty interesting fish! Here's more information about them:
http://www.planetcatfish.com/catelog...dont/334_F.PHP
The lobster is a cool idea, but if it's like the crayfish, it will eat your fish if it has the chance. Also, if you have any live plants in the tank, again if it's like the crayfish, it will destroy your plants. The lobster should probably be in a separate tank. I think they prefer cooler water also. As you can see, there are a lot of considerations to be made when purchasing the right fish for your tank. I think you should decide what is your showpieice fish first, and add other compatible fish around that fish. There are some great fish out there than don't have to cost a lot, and will bring pride and enjoyment to your tank. Please tell us more about what is already in your tanks, and please post your ammonia, nitrite, and nitrate levels, so we can help you get your tanks cycled. If you don't already have these tests, I strongly recommend you purchase an Aquarium Pharmaceuticals Master Test kit. It's on sale online at Petsmart. You may be able to copy the add online, and take it to your local Petsmart to buy it there at the sale price.
http://www.petsmart.com/global/produ...=1137416457174
It's great to have you with us! Please post back when you can!
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Ammonia is killing them. I can see them on the pictures exactly as you described them.