I am currently fighting a nasty, nasty cold of some sort which is reducing my brain to mush. To try to keep some kind of momentum going, I decided to post my notions on creating characters for this game.
Note that this is not a character sheet, and that I'm not yet prepared to accept applications.
Let me state right now that none of these are absolute, no exception rules. There's always exceptions that work well with these kinds of restrictions. My hope is that this list will help you shape your ideas to fit the milieu I'm creating, to save time and effort on your part from carefully crafting a character you love only to find out later it's not a good fit from the GM's POV.
1. No "historically-translated" characters. I'm not looking for a thinly-veiled Victorian Spider-Man or Victorian Wonder Woman. Those kinds of characters could be loads of fun in a different game; they're just not what I'm looking for in this game.
2. No famous contemporary historical figures, factual or fictional. Again, in other games, playing such characters could be a blast. Noting "wrong" with them, I just don't want the narrative baggage that could come with them.
3. No famous mythological figures. If you want to play someone whose origin is non-human, that's not a deal-breaker. But if you want to play a Faerie, you're not playing Titania or Puck. Again, narrative baggage.
I have no problem with characters using such figures as namesakes. For instance, an NPC you may encounter is John Barleycorn. He's not the actual personification of barley and the rhythms of agrarian life; he's just a dude from Sussex whose nature-related powers wax and wane with the seasons.
4. I am looking for heroes. If you have in mind a London street thief kind of character, they have to have a genuine heart of gold at the very least.
5. Your character needs to be at least somewhat social; brooding loners or silent, inscrutable noir-folk don't always work so well in a PbP environment, anyway, and character interaction is fun!
6. I anticipate that matters of socioeconomic class may arise during the course of the game, but I'd like to avoid super-snobbish gentry or violently anarchic chimney-sweeps. This doesn't mean that every character needs to be an all-encompassing, all-loving person – but to my mind there's a big narrative difference between a character who is, for example, an unrelenting snob who treats anyone from a lower rung on the ladder as dirt, and a character who is open-minded and learns from their experiences with people of other backgrounds.
If I could draw, I'd have you describe costumes to me, and I'd work with you to render the images. But I'm lucky if I can draw a bath, so that ain't happenin'. :D
A hero costume is optional. It could be something as simple as a typical set of clothes slightly customized for action, like a riding habit. For the most part, it should be more or less in line with the fashions of the day (in 1851, of course). However, feel free to stylize to some extent if you desire.
Given that this group of heroes is not a day-in, day-out team, you may or may not wish to create a separate identity. The Arcane Order of Pandora is not exactly a secret society, but they don't publicize their work, either. I'd say they're more on the QT than not.
Characters somewhat higher on the socio-economic ladder may have to consider their reputations in deciding to hide their identities.
Disguises do not need to be elaborate. In Anne Lister's diaries (she's the focus of the show Gentleman Jack), she repeatedly relates how, just because she wore masculine-tailored clothes, people would assume she was a male. It's not difficult to disguise your identity from most people.
The nom du guerre
Another way of concealing one's identity is to use a fake name or title. This is also optional. If you wind up wanting a nom du guerre for your character, consider giving it a bit of Victorian flair.
Using an "Accent"
I don't expect anyone to craft their dialogue posts in period English. If you want to give it a shot, go ahead. Just keep your reading audience in mind, and try not to let things go too Dickensian. Also, if you want to portray a certain regional or class-based accent, the occasional regionalism should suffice. I don't want to encourage stereotyping, but I also don't want a post so full of idiosyncratic language, contractions, and apostrophes that it's unreadable.