|When a Random Wizard poses questions, you answer!|
(1). Race (Elf, Dwarf, Halfling) as a class? Yes or no?
Absolutely. As others have pointed out, it makes playing a Human much more appealing, and I like me some Human-centric fantasy. Plus, race-as-class allows for some truly unique class options (like how Dungeon Crawl Classics does Elves.) I am toying with the idea of a very simple "kit" system ala AD&D 2E that would allow for some variety, however.
(2). Do demi-humans have souls?
Sure, why not? My fantasy world of choice, Uresia, pretty much assumes that everything has a soul--even the wind! I've never been a huge fan of resurrection or reincarnation magic, so the question didn't come up too often in my games.
(3). Ascending or descending armor class?
Descending all the way. Because if I'm going to be running old school D&D, why not embrace the idiosyncrasies?
(4). Demi-human level limits?
As other bloggers have pointed out, campaigns rarely last long enough for this to matter. But again, why not? (Plus see humano-centric statement above.)
(5). Should thief be a class?
Totally, as long as thief skills are treated as extraordinary versions of everyday activities. (Saying that only thieves can move silently or pick pockets is a bit like saying only fighters can swing swords.) As Rients points out, it's a class the DM needs to take a close look at, as they have a tendency to be either over- or under-powered depending on edition, but it's never something a little careful house-ruling can't fix.
(6). Do characters get non-weapon skills?
I use the skill system from Rules Cyclopedia to add a bit of spice, but if I want a skill-heavy game I'll play BRP.
(7). Are magic-users more powerful than fighters (and, if yes, what level do they take the lead)?
"Zero to hero" can get a bit overhyped, but when it comes to magic-users, I'm still a fan of a massively swingy power progression. Fifth level is the all-time classic milestone.
(8). Do you use alignment languages?
Lord no. I like my game worlds to have lots of different languages, but alignment tongues ain't it. (Outside of Celstials and Demons and such.)
(9). XP for gold, or XP for objectives (thieves disarming traps, etc...)?
XP for gold and carousing with secondary XP for monster-slaying, exploration, etc.
(10). Which is the best edition; ODD, Holmes, Moldvay, Mentzer, Rules Cyclopedia, 1E ADD, 2E ADD, 3E ADD, 4E ADD, Next ?
If we take "best" to mean "most concise presentation of the rules while still remaining true to the 'spirit' of D&D", then I vote the Cyclopedia. If we take it to mean "consistently best mechanical design", I vote 4E. If we take it to mean "purest", then I vote OD&D. If we take it to mean "the edition one feels most fondly for", it'd be 2E. The fact that none of those are my edition of choice tells me it's a pretty meaningless term.
Bonus Question: Unified XP level tables or individual XP level tables for each class?
Definitely individual. Dubious questions of "balancing" classes aside, it's just another one of those D&D idiosyncrasies I like so much.