A few notes on alignments:
First, I’m likely to allow, at most, one evil PC. Maaaaybe two, if two people manage to convince me they’ve got solid characters. And Chaotic Ridiculous is not an allowed alignment.
In general, the PCs should have sufficiently similar interests that they’re able to work together. (Bickering, of course, I expect that the first gaming session will include a lot of final character touches and deciding what your recent history together as the Adventuring Company has been like.
In the world itself, alignment is a known concept. It’s also known that alignment is more about religion, moral philosophy, and motivations, rather than actions.
As a consequences, while clerics and paladins and the like may Detect Evil and the other alignment axes, it’s considered impolite. Actually revealing someone else’s alignment is considered downright rude in most places.
Governments are generally well aware that Lawful Good people are capable of causing quite a lot of damage on the road of good intentions, while Chaotic Evil people may be are capable of contributing in positive ways to society (even if they may need extra incentives). Alignment-tests are not considered proof of guilt or innocence in trials; this is enshrined in law in all Five Nations and Life’s Edge. (It’s widely believed that being unable to accept differences of philosophy was a contributing factor in the Great Wars and the Apocalypse.) Alignment tests are usually only considered acceptable as tests for entry to religious orders or certain private organizations. Paladins who go around Smiting Evil without the victim being a clear threat will get in trouble with the local constabulary.
In terms of alignment, most people are True Neutral or Neutral Good. Lawful and Chaotic are equally popular. Truly Evil alignments are (a bit) less common than Neutral or Good (at least, among playable races). It’s also not uncommon for people to own amulets, rings, or other magic items capable of concealing one’s alignment (especially if Evil-aligned, but even the non-Evil may find this convenient given how relatively common the Detect spells are).
Postive/holy and negative/unholy energy, while typically associated with the Good and Evil alignments respectively, are not strictly tied to them. However, alignment-affiliated magic items and artifacts (such as, say, a +1 Holy Mace of Smiting) still have the expected negative effects on people whose alignment is opposed to theirs.
Most class restrictions are removed, but not all. If you’d like to play a class as a non-standard alignment, let me know. Some (such as for warlock and necromancer) are removed entirely, but the circles of druids are still unlikely to permit someone with too Lawful an alignment to join them, and monks are unlikely to be chaotic. Paladins always have one of the corner alignments, with flavor changes to match. If you’re unsure, check with me, and I’ll see if we can work something out.
Finally, only dragons, Outsiders (who might only be constructs of summoning spells anyway, depending on who you ask), and some unintelligent magical creatures have rock-solid alignments. Otherwise, just because somebody’s a vampire or a lich doesn’t mean they’re evil.
*** Addendum: Having reviewed the Detected <Alignment> spells, it’s important to remember that it takes 3 rounds of staring to get an actual read on whether or not someone is evil. I’ll also add an addendum house rule to this: For people who are not clerics of an evil (or <alignment>) deity, it takes an extra round to determine their alignment. Further, intelligent undead do not generally appear as evil. Finally, I will also allow the Detect Undead spell to be a learnable thing.