1. Filtration
A sponge filter and fluidized media in each tank should work fine for your filter.
2. Lighting
Discus don't need any particularly strong lighting in fact natively they're almost always shaded by overhanging vegetation. I would look into LED strip lights such as these:
http://www.amazon.com/s/ref=nb_sb_no...ords=truelumen
I am using two of the truelumen pro 48" lights to illuminate a 6' long 220 gallon aquarium. Their "Marine Fusion" strips are a spectrum of very bright white (12000 kelvin) and deep blue (453 nm wavelength). This color combo does not encourage algae growth and the deep blue gives the discus just a bit of a blacklight-ish shine which is very attractive. Makes the colors pop.
Truelumen sells their power supplies separately or you can buy just about any 24 volt 1.5 amp power supply. Most of these will be 60 watts, and 60 watts is enough for 2 48" lights or 3 or more of the smaller sized lights. Truelumen also sells power cord splitters so you can daisy chain the lights together. Don't buy the truelumen dimmer - nothing wrong with it, but buy this one instead since it comes with a remote and offers more dimming options:
http://www.amazon.com/Remote-Control...rch_detailpage
A word of caution, LED fixtures can be finicky about power. You have to understand well the requirements of the light strip and the power output of your power source. Read up on it and ask questions of anything you don't understand.
3. Water changes and how can i made them easy
You will want to get a large container to act as a common aeration tank. You can get something like a stock tank or rubbermaid garbage can container. Make sure it has the food safe plastic. This will need to be heated and have a powerhead or two (get the cheap ones) to move water around and aerate it. When you first fill this tank treat the water with Seachem Safe (or similar) and then after every water change when you are refilling this tank treat it again.
Other then a common aeration tank, you want to keep the various aquariums separate. Avoid mixing filtration etc. If you get disease or an issue in one tank you do not want to pass it onto all of them.
You can run PVC lines along your walls or the shelves of your racks with tees and valves leading to each tank to refill them after the water change. If you get acrylic or non-tempered glass tanks you can drill them about a 3rd of the way up from the bottom and install a bulkhead with a screen. Plumb all the bulkheads into a common drain line with valves. If you want to get fancy you can get electrically actuated valves so you just flip a switch and they all open. Let the tanks drain to the desired level and then close the valve. Open the refill valves and fill them back up. If you get tanks with overflows you won't have to drill the tanks although it's not hard to do.
4. Aquarium racks
There are tons of examples and designs for racks online and on youtube. I don't have an opinion here, just design your system to be modular, easy to move if needed, easy to add onto if needed, easy to run pvc lines and electrical lines.
5. Water making station
I described the common aeration tank above. This will be your primary water making station. As I've learned, a super low PH is not as important as a rock steady PH. Discus can do just fine in a high-ish PH as long as it never fluctuates. Measure your tap water. If it's super hard it will probably have a PH around 8.0. Plenty of folks do fine with discus at 8.0 but if you do want to lower it you'll need an RO filter system. Look at RO Buddy on amazon they are good systems and inexpensive. I have the 100 GPD model. RO water should be around 7.0 PH. You will want to mix mostly RO water with some non-RO water so that minerals are not depleted from the water. A RO system produces 'waste' water which is basically concentrated with all the minerals that the RO filters are removing from the tank. I am currently pumping about 20% of this 'waste' water back into the tank to supply minerals.
As an alternative to a large aeration tank, you could install an on demand water heater (a smaller model is only about 150 bucks) and a thermostatic mixing valve. The mixing valve will output water at your desired temp (I do 82 degrees f) and put it through the RO unit. Then it can go straight into your aquariums. Keep in mind to be most effective you will need a very large RO system otherwise it will take way too long to refill your aquariums after you drain out water for the water change.
6. Electrical support
Its true all this equipment takes a lot of power. Add up the amp needs of all your equipment and make sure your breaker will handle it. If not then install a breaker box sub-panel in the fish room (consult an electrician).