My answers to Random Wizard's questions.
Race (Elf, Dwarf, Halfling) as a class? Yes or no?
Of course yes, as long as I use any character classes.
Do demi-humans have souls?
Of course yes, because they may trade / lose them!
Ascending or descending armor class?
Demi-human level limits?
I don't know! No one ever survived long enough!
Should thief be a class?
Do characters get non-weapon skills?
Are magic-users more powerful than fighters (and, if yes, what level do they take the lead)?
It depends but there's no general rule. There are spells capable of wiping out entire cities but swords don't run out of charges / slots.
Do you use alignment languages?
I don't use alignment system so I guess nah.
XP for gold, or XP for objectives (thieves disarming traps, etc...)?
Gold and slaughter. And, of course, carousing!
Which is the best edition; ODD, Holmes, Moldvay, Mentzer, Rules Cyclopedia, 1E ADD, 2E ADD, 3E DD, 4E DD, Next ?
For me? 0e.
Unified XP level tables or individual XP level tables for each class?