Undergravel filters are kind of old school. They tend to become Nitrate factories but keeping fish waste and other debris trapped underneath. I found it much easier to just vacuum my gravel once a month. Not only do you remove the need for airstones and power heads but in the long run keeps your nitrates down. I prefer using canister filters and HOB filters. Wet/dry sump systems if the tank is drilled. The LFS is probably clueless about it cause they aren't used much anymore.
As far as your filters, I have never used the MAG 350's. But what I can tell you is that charcoal/carbon are useless unless you are removing medications that you may have dosed in your tank. So I hate to see you spend your money on something that you really don't need on a regular basis. The charcoal only lasts a week or two anyway. And in the other filter, I'm not really sure what you mean by that this filter is for ammonia only?? If you are running ammonia removing media, again it's really not needed on a properly cycled tank. Your filters biological media (housed with good bacteria) will take the ammonia and turn it into nitrite. Another good bacteria then takes the nitrite and turns it into less toxic nitrate which is removed during water changes. Ammonia removing media or liquids aren't needed unless you have an ammonia spike in your tank for some reason and you're worried about loosing fish. Again not sure how the set up is, but it would be more benificial for you run more biological media rather than carbon and ammonia removers.
Also if you are considering African cichlids you may want to look into using sand. Very natural looking and easy to keep clean. Unlike undergravel filters which you have to tear down the entire tank to clean. Hope this didn't confuse you any, but just thought I would let you know other more modern options.
As far as your filters, I have never used the MAG 350's. But what I can tell you is that charcoal/carbon are useless unless you are removing medications that you may have dosed in your tank. So I hate to see you spend your money on something that you really don't need on a regular basis. The charcoal only lasts a week or two anyway. And in the other filter, I'm not really sure what you mean by that this filter is for ammonia only?? If you are running ammonia removing media, again it's really not needed on a properly cycled tank. Your filters biological media (housed with good bacteria) will take the ammonia and turn it into nitrite. Another good bacteria then takes the nitrite and turns it into less toxic nitrate which is removed during water changes. Ammonia removing media or liquids aren't needed unless you have an ammonia spike in your tank for some reason and you're worried about loosing fish. Again not sure how the set up is, but it would be more benificial for you run more biological media rather than carbon and ammonia removers.
Also if you are considering African cichlids you may want to look into using sand. Very natural looking and easy to keep clean. Unlike undergravel filters which you have to tear down the entire tank to clean. Hope this didn't confuse you any, but just thought I would let you know other more modern options.