Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
If you like canisters, then go for it. They do fit better under the tank, less visible. There are some pretty good innovations out there in the last few years.
Similar can be said about LED fixtures. Have a look in the Lighting forum for a lot more advise.
There is no cheap and efficient CO2 system. The tried and true is still a bottle, regulator, needle valve and good diffusion method. Often the diffusion is combined with the filter, especially if you select a higher flow canister.
If you try to downgrade the canister to 'just barely works' then further impede the flow with more plumbing you can dip down into 'does not work very well'.
Mollies are hard, alkaline water fish, salt is optional.
Kuhlie Loaches are soft, acidic water fish. Not compatible.
Catfish is a giant fish family; which ones are you thinking about?
Plant choices: Almost all the plants commonly available for aquariums are compatible with a wide range of conditions. There are a few specialty plants that really do need soft, acidic water, but these are usually noted as being special.