Ah biotope ... now you are talking my language
. As BWG said the are no annoying questions, it is good you are doing your research. Let's be honest, there is a lot of conflicting (and even just plain out-and-out wrong) information out there. There is no better propagator of misinformation than the web.
Considering the Rams, if you went for the Blue then you would really be looking at a SA biotope or if it was the Bolivian then you could go down the Amazon route. The reason for this being that the Blue is a native of Venezuela, there are reports of it being found in some of the Brazilian drainage channels but these are largely unsubstantiated.
I would recommend sand as a substrate rather than gravel as this will be beneficial to the fish. No need to take out all the gravel, scoop some out and replace it with sand. In time, the gravel should start to work its way through the sand and give a 'natural look' (not strictly correct for the Amazon but hey-ho it is impossible to do a 100% accurate biotope anyway).
Rocks are very rare in the Amazon, so rare that in many places they are used as currency. Wood is far more natural and don't think you have to pay the ridiculous price in fish shops, a wander around your local woods can give you several suitable pieces which can be prepared to go in the tank.
The other decision you have is Blackwater or Whitewater. Blackwater is so called as it is stained with tannins from decaying leaf matter, wood etc. (takes on a tea like appearance), whitewater isn't stained with tannins. Most SA species will display enhanced colours when in Blackwater compared to Whitewater and they mostly tend to prefer 'dimmer' lighting which Blackwater will create (floating plants are also a good consideration).
Fishwise BWG has pretty much covered it. For the catfish you can look at Corys, Brochis, Whiptails, Otos and even Plecs (pretty much anything can get swept into the pools during the floods but I would bear in mind the demands of some of the Plecs and, remember, a lot of them are wood eaters and will require it in the tank). You could also throw in Headstanders. Trying to think of anything else and other than the Angelfish that you suggested my mind has gone blank at the moment, sorry. I have omitted things like Discus and the larger cats as I get the impression you aren't thinking along these lines. If you do decide to go for a shoal of Tetras or the like then I would (personally) say go for the largest shoal you can rather than the usual 6 or so. I have 30 Cardinals and they just behave in an entirely different way in larger groups.
Below is a link to the thread containing my first ever post on the forum that you might find useful (just bear in mind there are many, many more) South American plants
Keep asking away, pretty sure we can get you on the right lines between the pair of us