OK slow down for a second.
I have been hesitant to respond to this one because there is no easy answer, but here goes.
First check out this post which will show you one very good design on how to build your own sump/fuge and is basically what I followed:
http://aquariumadvice.com/viewtopic.php?t=53046
You can use any size tank and then adjust the plan to fit. I would not recomend anything smaller than a 20L for your tank.
You will need an overflow and a pump and a container to function as the sump(can be abother aquarium or even a rubbermaid tub). The key is to get an overflow that is rated to handle at least the volume of water your pump is returning and preferably more. Remember to look at the rating for the height you will be pumping usually 3-4'. This is where some get confused. It does not matter how much the overflow is rated for as it will not drain more from you tank than what you are pumping back into it.
Ideally you want to have at least ten to twenty times the tank volume for a flow rate. In your case you would want 550-1200gph flow. This can be accomplished with the sump pump, power heads or better yet a combination. So if you get a sump pump that is rated 600gph your overflow box needs to be at least 600gph and probably more. I use a rio 3100 which is rated about 800gph and can be obtained for less than $70.
The overflow box is basically a device which creates a constant siphon from your tank to your sump and then the pump returns it to the tank. If you get a good one the sipohon will restart on its own if the power goes out. Otherwise the sump could overflow or the main oveflowing once the power comes back on if the sipon does ot restart. So the pump and overflow you do not want to be cheap with. This is why I opted for a predrilled tank since it was about time to upgrade anyway. I have heard the CPR models are very good, but cannot speak from experience as I do not have one. I priced these at the
LFS for $100-150 for the highly rated models, but I am sure you caqn find them cheaper online.
The sump itself can be a very simple tub or something more complex like in the link above. The sump basically just increases the water volume of your sytem and provides a place to put unsightly equipment like filters, heater, skimmers etc. A sump can also be a fuge or contain a fuge area which can be lighted to propogate
pods, corals, or house other critters that might be devoured in the main. For example I keep LT rubble and grape clapura with a
DSB in mine to help reduce nitrates and produce
pods. I also keep a light on mine 24/7 which helps reduce
PH swing. The other big benefit of a sump/fuge is that it adds water vo,ume to your system. The more water you have the more stable it will likely be.
So in simplistic terms you are creating a loop in which water is drained from your main tank via the siphon (overflow) to a sump. Flows throught the sump (and fuge if you opt for one) and is then is returned to the main via a pump. The water in the main does not overflow because it is being drained at the rate it is pumped into the main by the overfloe box.
Now one final caution. You do not fill your sump all the way up. When you initially set up your sump you need to conduct a couple of power outage tests. If set up properly when the poer goes out you main should drain down to a point where the siphon breaks and all the water should fit in the sump. When the power starts back up the siphon should re-establish and the system keeps running.
It seems real complicated, but once you play with it really it is not. Personally I waited two years before setting up a sump/fuge and wish I would have done it from the start.
Here are a couple of related threads:
http://www.aquariumadvice.com/viewtopic.php?t=65613&highlight=
http://www.aquariumadvice.com/viewtopic.php?t=62045&highlight=
http://www.aquariumadvice.com/viewtopic.php?t=65122&highlight=
Bottom line, some of your questions cannot be answered. You need to do some reseacrh and figure out what is best for you system.
HTH,
