The substrate is extremely important for the health of the aquarium. You need some sort of "gathering place" for waste so the various bacteria [not talking about nitrifying bacteria here] can break it down. This is crucial for the biological system, and also provides nutrients for the plants.
The pebbles you mention are too large to provide a good biological bed. They can be used "on top" but not as the sole substrate. Plants will also find it next to impossible to root in these, especially the sword; Echinodorus develop very large extensive root systems, and they must have a substrate of sand or fine gravel. The largest "gravel" would be what is called pea gravel, or Birdseye, as the gravel particles are roughly the size of green peas. I have tried this pea gravel and found the substrate-rooted plants (crypts, Vallisneria) did not do as well in it as they do in the finer gravel and sand, but it should work for swords.
Kangy is going in the right direction. I would suggest a base layer (about 2 inches) of fine gravel or pea gravel, then sprinkle the pebbles over it after you plant the main plants (swords and cabomba from your list; Anubias by the way should be attached to rock or wood, the rhizome should not be buried or it can rot). River rock (pebbles and slightly larger sizes) scattered on top can create a very authentic and lovely river habitat. I have something along this line in my 90g, photo attached; gravel is a fine dark mix. And for another example, the second photo is of a Central American stream layout from Peter Hiscock's book Aquarium Designs Inspired by Nature;
gravel here is natural (tan/buff mix) pea gravel. You can also get pea gravel in the dark identical to my tank.