Are mutants common? Not at all. There are currently approximately 6,000 mutants known to government officials, a number which is unofficially estimated to be about half of the number of mutants in the country. About 1,100 mutants are currently held in government facilities of some form or another.
What is the current general opinion of mutants? Mutants are still considered a new threat, and considerably dangerous. The response to this is a general hatred toward them that most mutants experience first-hand. Using mutant abilities in public is extremely dangerous and if it does not attract the attention of law enforcement, it will almost certainly attract local anti-mutant organizations or mobs.
Anti-mutant rallies are common, and for characters who regularly traverse into town they will almost always see groups of people on corners with anti-mutant signs. The construction of the school has seemingly only made things worse despite the fact that it essentially keeps mutants away from the general populace. Such protestors can even be seen from time to time gathering at the gates of the school.
What is the official governmental stance on mutants? Mutants are officially considered to be a severe security risk to the safety of the citizens of the United States of America, and are mandated to register their names and mutant powers with the federal Bureau of Mutant Affairs, as outlined in the Mutant Registration Act. Currently, there exist tactical strike units trained to deal with superhuman cases and there is a prison, the Vault (located in Colorado) which is equipped to detain mutants.
Under the Mutant Registration Act, mutants are required to identify themselves as mutants to qualified law enforcement, bureaucrats and health care professionals. Employers in industries views as 'sensitive' are allowed access to the Mutant Registration Act's database by applying to the Bureau of Mutant Affairs. Employers, insurers and similar private-sector individuals are permitted to deny employment or services to mutants whose powers are considered 'dangerous'. Government services of the state and federal levels are required to offer services to mutants, however.
However, there is no systematic government effort to round up mutants forcibly, at least yet. The Kelly Academy is a pilot program, which is likely to be expanded into a nation-wide network of mutant schools. It is the current intention of the Kelly Administration to make these schools mandatory for the mutant population once there is enough capacity to meet demand (of the 12,000 or so mutants estimated to be in the country currently, over half are under 18). There are also plans to create a college for the training and education of adult mutants.
It is difficult to gauge the true feelings of President Kelly, but he does not appear to condone the more radical activities of anti-mutant groups, being motivated by what appears to be a genuine concern for the security risk that mutants pose to America. He has expressed a belief that mutants are as dangerous to themselves as anyone else and that the Mutant Registratoin Act serves to protect them as much as restrain them.
How many students are on campus? While the school was built to be very large for the eventual influx of mutant students who would be attending it's still fairly new, and mutants in general are fairly rare. While the school can have an estimated 800 students at maximum, it currently only houses approximately 250.
How does the school network work? The school network is essentially a private forum for the student body. Students and faculty can create accounts to post privately for themselves, to the general public, or to specific people. They can also create dummy accounts (via the subchatter community) to spread gossip or simply post anonymously.
What about Xavier's school/The X-Men/the Brotherhood? Charles Xavier is a respected intellectual and mutant advocate, but has never operated a school for mutants. No formal organization of mutant resistance to the government has been proven to exist, though there are doubtless references to a 'Mutant Brotherhood' in the blogs of rabid anti-mutant activists.
Do you allow characters who are not canonly mutants? Yes, but only if they can be reasonably rewritten for a mutant backstory.