Human Multiclassing

The Lamentations of the Flame Princess game I am working on will largely be focused on humanity.  I'd like the characters to be drawn exclusively from Clerics, Fighters, Magic-Users, and Specialists.  However, I'd like to keep the game in line with a bit of the Swords & Sorcery paradigm of the heroes being good at many things.  What does this mean?  Multiclassing.

Each one a Fighter/Thief... and Human

I know that the B/X rules didn't have any type of multiclassing in them (unless you are an Elf, of course), but here are my initial thoughts on the deal:

• Characters do not begin the game multi-classed.  I'm not 100% tied to this one.  Maybe work multi-classing at the beginning in with the character's background.
• To be eligible to learn a class, they must study under a teacher for an as-yet-undetermined time (with an as-yet undetermined cost) which grants them level 1 in the class studied (I think I'll tie this in with some of the rules from the Hill Cantons Compendium, found over at... Hill Cantons).
• When you have multiple classes, your experience points are spread equally among the classes you use in an adventure.  This means that if a Fighter/Specialist goes a whole session never getting in a fight, but uses his Specialist skills, all of the XP gained go into Specialist.  With the ubiquity of Fighter and Specialist skill usage, there won't be the question of what happens in a role-play only session (not with anyone *I* have DM'd for, at least).
• Of course, since I have aligned Clerical magic with Law and Arcane magic with Chaos, there will be no Cleric/Magic-Users in the game.

Since all of the players will be humans, they will all be on the same page for these, and there shouldn't be much of a competitive edge.

Any thoughts on this?