1) There are no level restrictions for player characters. Non-humans who reach their maximum allowable level can still gain levels but they must pay twice as much XP. For example, if a PC needed 100,000 experience points to get to the next level normally and they had already reached their maximum allowable level, then it would take them 200,000 experience points to reach the next level.
2) Dual-classing is not restricted to human PCs. My opinion is that the main system is backwards. Humans don't live as long and therefore they would try to learn all they can at once, so they should have the multi-classing ability. Demi-Humans have the time to focus on one class then focus on another and should be the ones with the dual-classing ability. Therefore, demi-human races can dual-class using the same rules for normal dual-classing. There are some human races that have the multi-classing ability as well, you will find them on the extras page
3) Instead of using the memorization rules for spell casting, Lands of Calidair will use a Spell Point system. What this means is you still use the spell progression for how many spells of each level you cast, but you choose the spell at the time of casting. IE: a 5th level mage has a spell pyramid of 4 1st level, 2 2nd level, and 1 3rd level spells, therefore instead of memorizing 3 magic missiles, 1 detect magic, 2 stinking clouds, and 1 fireball, the mage can cast 3 of any 1st level spell he has, 2 of any 2nd level, and 1 of any 3rd level. Mages are restricted to being able to cast only those spells in their spell book (spell books must be turned in with character sheets). Clerics are allowed to cast any spell from any AD&D published 2nd ed book or Dragon Magazine. Certain Cleric spells from modules and other sources can be used on approved basis. In addition to the spell pyramid, the spell caster also gets a few extra spell points. Mages get it from their Int score, Clerics from Wis. Take the appropriate ability number and divide it by 3 to get the number of extra points. The caster can use these points to cast spells using this formal: 1 spell point per spell level used. This means a Mage with an 18 Int has 6 extra Spell Points and can cast 6 1st level spells, 3 2nd level spells, 2 3rd level, etc....any combination that adds to 6.
4) We are starting to get more defined rules for our tech side of the game. You can find these rules here: Tech Rules