I entered my votes above, but wanted to expand on a couple of them:
1. Weak, Atmospheric magic: I chose this because it seemed to be already assumed in your setting blurb. If you've got a high-magic world someone could, say blow up the king's castle with a powerful ritual, then the world would have to be designed with that level of magic in mind. It couldn't just be Prussia, 1844, plus magic, because there would be too much in our world that just doesn't make sense in a world with common magic. I think someone touched on that further up the thread.
2. Non-restrictive archetypes: I can take or leave classes in a game, but I think you absolutely need to have something that gives the players an idea of what sort of characters they're going to make. Even assuming that everyone has a copy of the rulebook (once published), the players are going to skim over almost all the setting detail and focus on the rules. Within those rules, you need to have several things flagged that point them to what sort of characters are acceptable within the setting.
Similar to this is the question of what the characters will be doing, if everyone is playing a revolutionary. It's certainly possible to have a game in which every PC is a revolutionary sorcerer. It wouldn't be all that different than having a game in which every PC is a soldier or a superhero, and those get played all the time. The key is to make it so that sorcerers, revolutionaries, and PCs aren't carbon copies of each other. Within this theme of the game, give people plenty of room to maneuver to make the sort of character they want. The mention of the "alignment" is a good start- PCs will have different reasons for revolting, and different outcomes they want from the revolution. There could be idealists, rabble-rousers, power-seekers, etc. Other possibilities for character differences are career paths, different types of magic, social or regional backgrounds (though you'll want to be careful of how you handle this with RW areas), etc.
I definately think that you should have options for non-sorcerous characters. A different FX system might be the way to go. If religion is a heavy theme of the campaign, then you could use the old arcane vs. divine opposition to come up with Faith type rules for miracles, healing, etc. For mundane characters with no powers at all, I would look at something like the drama point systems in Buffy and Angel- essentially, the mundane characters get to use drama points to boost their luck and effect the outcome of things. The supernaturals wouldn't be able to do this primarily as a mechanical balance issue. The story reason could be something like, using sorcery drains one's "luck", while those who do not use sorcery are free to make their own luck.
As for porting between tabletop and LARP, it could be possible, but will take careful planning. IME, systems which work well in tabletop would be too complex for LARP, and vice versa. I would focus first on the tabletop aspect, and then work on trimming things down for LARP. You can still use the same mechanics, just simplified. Even D20 LARP is theoretically possible, provided that you find ways to streamline character creation and cut down on oddball maneuvers like bull rush or sunder.
