1) If you can think of any historical civs or mythical cultures that you might like to see in Adventure mode, please suggest them...
Can't really think of any that haven't been suggested already. If possible though you might make the different groups generate citys slightly differently. An example would by like my most recent fortress that's been going for a couple centuries. Started out with major aquifer problems, so I ended up building a massive surface fortress, later I realized that it was 2 steps from being Osaka castle. Though most adventuremode players probably don't search out the amazing architecture of towns and forts.
2) Do you spend much time playing adventure mode to hunt semi/megabeasts, titans etc?
Honestly only started getting into it a couple weeks ago after my travel laptop lost all ability to play my sprawling fortress. As the hunting megabeasts and such. All the time now after my character is reasonably strong. Thankfully, a visit to my castle netted me a nice artifact steel longsword (produced in like year 12, and now its almost ancient being in year 326) and I travel around playing like a Paladin character hunting the greatest evils of the land.
3a) Does attention to detail matter to you in adventure mode?
Not that extreme, but a little note here and there is nice. For example if you can do it, make it so greetings between other cultures are in their respective languages. Nothing too hard. Just like if you visit a Russian shop they greet you with "Dobro pozhalovat", A german place would say "Willkommen", and visiting Japan would net you an Iirashimase. Or something (don't sue me for spelling, sry I'm not a linguist)
3b) How would you feel about culturally specific weapon, clothing and armour variations, or would you prefer to play where the variations are limited for simplicity? (Ie one type of axe used by all civs)
As sad as it is most weapons are all the same, though the game does lack a broadsword, Heavier then a longsword, and thus slower, but more ability to knock an enemy off balance. And a good straight bladed spear, (glaive, naginata, volge) thats primary attack is a slash rather then a stab. But since the game doesnt model wide swinging attacks that could hit others, it's not that much more effective than a halberd. (if it did 2h swords would be much much better than they are now. Also weapon parrying needs to be worked on, though i think thats planned to go with the "fighting styles" in the future)
Last but not least is the sling, as a method to boost damage from simple rocks. If you've ever tried an "early" game (start before about year 50) arrows can be few and far between, so for combat most players train up their throwing, and just chuck weapons or rocks.
4) Should elves and goblins be removed if other races can fulfill their contribution to the DF world?
Nah leave them.
5) Do you ever use the pommel strike and blade slapping attacks with weapons?
All the time. Its actually the best way to train up sword, spear, and axe skills, because it can give you much more time to attack the opponent before they die. (ofcourse, make them lose their own weapon first)
AND MOST IMPORTANTLY
6) Why do you play DF Adventure Mode? What is it, exactly or generally, that you like so much about DF Adv Mode?
Well initially because this laptop doesnt have to power in it to play fort mode (which I've played for several months) to excess, but really I find adv mode refreshing. Its kinda annoying early on when your characters worthless though, but its kinda fun to make a guy and think that you're affecting the future of this little world. After the next patch my general plan is to start a hero on year 5, and play him for as long as I possibly can. Then build a fortress over his grave and have hundreds of engravings to that hero.
I dunno though, it reminds me a lot of playing good ole Nethack. But the added bonus of being able to attack parts as needed just makes play so much more interesting. Like I said before I play my character like a "knight" or "paladin" of other games. Go from place to place destroying evil. And I even go so far as to not kill wild animals unless they attack me first (hundreds of wolves killed). When it comes to fighting humans and goblins, I try to break their arms or hands with sword slaps or shield bashes, and if possible, I just leave them injured, and leave. Really on this character I have only 20 humanoid kills for a person with 2 dead bronze colossai, hundreds of zombies/skeletons, and a couple dozen misc megabeasts (the giant iron badger with poisonous blood was particularly annoying, though his blood has proved useful.)
Long story short though, good luck on your mod. When it comes out I'll try it out.