As for the not sure what is required. Here is outline for characters we used before, subject to Lancis's revisions of course.
Also, check out the following. http://www.hp-lexicon.org/
It is a good resource for general information.
As for the tone of the game. Given the chosen time frame, think of it like post World war 2, trials and all.
For those that sided with the ministry and tolerated/liked muggles the great enemy is dead and his underlings are getting rounded up and brought to justice. Years of terror induced by "you know who" and his death eaters are coming to an end. You know who being Voldemorte, but he was bad enough that even the Aurors, basicly a mix of FBI and US Marshals, won't even speak his name. Think of him like all the bad parts of hitler, but able to walk through london and Washington DC and no one able to stop him from wrecking havoc, scary SOB. So all in all, this is actually a happy time, there is pain and sorrow but the guy is gone, beaten by a baby boy of all things, the boy who survived the killing curse.
For the Death eaters, their family and any sympathizers to their cause, it's like the end of the world. They are being hunted and persecuted. They have to hide their beliefs, lie turn in other people. Their great protector and leader is gone and suddenly there is no power struggle, the other side is just running them over. Lots of their friends/heroes are going to a prison that rivals hell, because at least in hell you can remember good times, here everything that brings you joy is sucked out of you, miserable place. They are trying to adapt and continue their work, but now they have to do it in very guarded secret,much more subtle as they lack their awesome protector.
As with our world their are elitists and open minded people, there is also racism, but skin color isn't the determining factor, what the bigots care about is the purity of your blood, like nobility, how many generations back are your ancestors wizards. Europe, Asia and Africa are in about the same standing as wizards. The Americas and Austraila tend to be assumed to not be pure bloods because most of the Native wizards were killed when the muggles and wizards from europe landed and the ensuring conflicts, or they were so integrated with their people that the european wizards couldn't tell them apart. The Europeans that went to those regions tended to be poorer and needed to find room to make their own stake.
The Houses within the school are formed from the 4 founding members of the school. You can find more on that in the site provided above. One important thing is the long standing Gryffindor/Slytherin rivalry. It goes back to the founding members of the house. The other house is distrusted/disliked based entirely on principle. While exceptions maybe made for specfic people, no member of the opposite house is like by their house and the other house as a whole or even in the majority. Raven Claw and Hufflepiuff seem to walk the middle ground, not having any major rivalries, but slytherin and Gryffindor are always in a state of official cold war. They are kids, so they aren't going to exterminate the other house, but they'll play pranks targeting the other house as a whole.
That's a run down, anything more specfic can be answered on a case by case basis, so ask away. I'll honestly admit I'm a 22 year old male who is way to into this series for my age.
top 3 fantasies:
Don’t put dragons down, Hagrid couldn’t have one, you can’t have one.
Phoenixes… ask Lancis before it goes into the profile, not after.
Pets who get in trouble can get sent home, or if particularly yappy used to replace the Quaffle at the next quidditch game.
things you should include:
What they have been like in the school up until this point
Family quirks. (family is eccentric or uppity)
Status. (Rich or poor, Pure blood, half blood muggle born)
Anything the school population should already know or could with little
Anything the school should specifically not know about the student
(make sure to state they shouldn’t know)
Any toys or special qualities worthy of note