New tank advice needed

I've been lurking here, reading posts for the past couple of weeks and have
read the FAQs and now need some advice about a proposed new tank. My present
tank (my first one) is a 20-gallon with 10-15 plants (swords, vallisneria,
pennywort, etc.) and a golden severum, a couple of silver dollars and a few
barbs. The fish and I have reached an accommodation: I give them romaine
lettuce and they keep their munching on the plants to a minimum. The plants
are doing well.
Within the next two months I plant to move up to a 75- or 125-gallon tank
(depending on
how much money I decide I can spend. I plan to have the tank pretty heavily
planted most likely with South American plants. The fish will include the
present ones and new ones for a community tank.
I don't plan to use an undergravel filter as I want to incorporate laterite
into the substrate,
along with heating cables using plans from the July Aquarium Fish as soon as
I lay my
hands on a copy of the magazine. I also plan to use CO2 injection using the
yeast method.
Despite all of the reading I've done, I still need advice on filtration. The
tank will be in
the living room, so I want something that won't be noisy. My thought has been
to go with an Eheim canister, though I don't know what a proper size would
be. Or would Magnum or Fluval or some other brand be better? Would just a
canister suffice or should I use some type of box filter in conjunction with
it? Will a spray bar be a good idea or will this provide too much water
movement for the plants?
Also, where can I buy laterite?
Thanks for any help, and I want to say how much I enjoy reading your forum.
informative and it's nice to see everyone exchanging information without any
Phil Marty