Canister filter advice needed (and other).

Background.  I've had fish around for 4 or so years but now I want to have a nice tank with plants and fish.  I've been able to raise some plants but usually they die within 2 months.  Actually in my 30 gallon tank most plants seem to live as long as I don't put to many in and the occupants don't decide to have a feast.  I currently have a 30 gal tank and a 40 gal tank running.  I've raised assorted fish and raised a couple of batches of Angelfish a couple of years ago.

I'm setting up a 55 gallon plant (and fish) tank and want to use an external canister filter.  The only filters I've used before are sponge and the hang on the back of your tank type filters.  Anyway I'm wondering which brands are good and good values.  I've been looking at a catalog from Pet Warehouse and see they carry Magnum, Eheim and Fluval.  My plans for the tank are to have it planted pretty densely and have 2-6 black angelfish, 2-4 kribs, 6 or so assorted small (1-2") fish and maybe 1-2 bristlenose plecos or SAE if I can find some.  Would someone be kind enough to explain the advantages/disadvantages of these brands/types of filters?  Do any of them make it easier to inject CO2 into them (or maybe that is bad to do anyway)?  Oh, the tank already has 2 holes drilled/cut in the back of it for filtering.

Substrate questions:
I planned on having 2-3" of Jim Kelly type substrate (sand and vermiculite (sp?)) with 1" or so of "gravel" on top.  Or would I be better off with just 3" of gravel with some laterite mixed in?
I already bought the gravel (200 pounds worth) from a sandblasting company.  I did some pH testing (1 cup gravel 2 cups water) on it and it did raise the pH of water out of my water conditioner .5 (from 7.5 to 8.0).  I'm testing again with a mixture of "soft" water with "tap" water since that is how I normally fill my tanks.  Is this bad?  I'm thinking of doing CO2 injection so I figure I could get the pH back to 7.0 or 7.5.

Other hardware I'm planning for the tank are:
4 40 watt tubes for lighting (if this is too much I'll go down to 3 or 2 tubes running.
Some heater (maybe in the filter).

I hope that the cabinet for it will be finished this week or early next week and so I'd like to order the filter in the next few days.
Sorry for the rambling on.

Don Griffes
dgriffes at coresoft_com