I`m going to say yes to both of these questions, as everything we've seen points out to two of the same species of digimon at levels higher than rookie(champion for beast types) is extremely rare. As they grow as individuals, their evolution seems to follow a path more set by their own beliefs and experiences rather than a set line.
Also, digimon differentiate more as they evolve. "villages" we have seen are often made up of rookie digimon who have not yet differentiated into individuals yet.
From this, I'd go out on a lirab and say there are infinite species/possibilities for digimon evolution, since everyone's lives follow different paths.
Armies of a certain type of digimon make sense, as rookies who were raised together for a specific purpose would follow the same evolution line.
On another topic, I`d like a decent digimon game for once, one NOT based on monster collecting games and actually having a format similar to a season of the show, with a party of different tamers/digimon that you follow in the world and use to fight at the same time.
I could probably see Tamers being made into a game using the Persona 3 Engine/gameplay style, with digivolutions taking the place of personas.
Because Savers is a different universe, that Gallantmon likely evolved on his own, and in that world, rather than being a result of Takato's fusion with Guilmon, Gallantmon is the(a) natural result of Guilmon's evolution.
Finally, I`d like to say that Bandai puts too much focus on sales of the Digimon Virtual Pets/ carRAB rather than material related to the anime itself. They've done a great job of keeping the focus off of merchandising in the shows(one thing that sets digimon apart from other toyetic series is that there has never been a digimon tamer tournament or other such ilk, it's all focused on plot), but fail to seemingly realize the quality of the anime itself as potential for tie-ins other than charachter songs.