Because this will be in B/X it means a "dwarves, elves and halflings are classes" structure. So I need to deal with a couple of inevitable questions:
1) why don't the demi-human races have clerics?
The gods of this world are the stars overhead, and when they meet as pantheons they meet on one of the three moons (there's an interesting split in human religion over whether the sun counts as a god). The three pantheons are the gods of the Fae, the Gods of Humanity, and the Gods of the Earthfolk.
Well, there _were_ three pantheons. The Fae gods stars are occluded by a cloudy formation in the sky, their moon is in a geostationary orbit over the elf city of Deephome. No one knows what happened to them, and it has been this way for as long as humans have records. The elves (and the halflings who are more fae than earthfolk) have no clerics because they have outlived their gods.
The earthfolk gods take created not just the dwarves, but also the giant-kin, which includes orcs. As the gods of the earthfolk became twisted, the dwarves broke with them, and the enmity between dwarves and giant-kin is greater than you can imagine. The dwarves (and those halflings who are more earthfolk than fae) have no clerics because they are apostates from their pantheon.
2) Why can't dwarves and halflings wield magic?
In play, I'm actually tweaking halflings to make them less Tolkien and more faerie, and the player will have a choice to give them the choice of some magical powers, and have them be satyrs, dryads, kitsune and other nature spirits, or additional durability and have them be more classic halflings.
Dwarves don't have wizard like spellcrafting, but will gain Dweomercraft as a power that lets them create and forge magic items. This takes a long time and is very expensive, so it really only comes up at level 5+ play. Earthfolk just don't interact with magic the way humans and elves do.
3) Alignment?
I'll be stealing a page from 13th Age here and rather than Law/Neutral/Chaos the PCs will have a list of 9 major patrons whose clearly defined goals the PCs can align with. Each patron's followers have common phrases and signs to act as an "alignment language", and when you meet someone of your "alignment" you'll be able to get extra assistance from them.
Alignments Include
"The Lost King": restore humanity to where it was before the giant's shadow fell
"The Matriarch of the Moon": leader of the organized human religion... in the north at least...
"the Lord Mayor": forge a new direction for humanity based on the facts on the ground
"The Elf Court": very conservative and systems driven, more on the side of the Lost King
"The Dwarf Counsels": balanced between tradition and innovation, more on the side of the Lord Mayor
"Queen Mab": The secret name of the loose ruler of the thieves guilds, likely a halfling if she exits at all
"The Clouded One": the cloud giant tasked with maintaining the edict, watching overhead.
"The Brotherhood of the Stars": leaders of human cults, each deeply grifting their own congregations
"The Orc Kahn": Chaotic strength/violence proves leadership, forget the edict, take it all.
If you're thinking "hey, that kinda maps to the 9-fold alignment chart, that's by design.
