Monk will definitely be my first character. Just seems to fluid but powerful but supporty but tanky but evasive. I just think they have a great variety of abilities that look like a ton of fun. I can't wait to play!
WD will have to be my 2nd play through. As soon as I saw the Monk I was addicted but I have always loved characters with summoning abilities and I feel the WD will provide that fun when I decide to stop playing my Monk for a little bit. Who knows though? Maybe he will become my main in the end.
The Diablo Universe has no need for a DPS meter. The game is about hack and slashing through the unknown and not about min/max about how to continually push the top. There is no need to make players feel pressured into select builds to succeed.
I want to play a heavy hitting, damage Monk and probably will through the lower levels of the game but I'm not 100% sure how it will work out in Hell/Inferno (if I make it that far). I personally feel the Monk has a lot of utility that needs to be used in balance. In the end, I'm sure I'll be putting out fair damage while healing so I'll be a "true" Monk.
As everyone has stated previously you can easily swap skills so you won't have to have multiple characters of the same class (Ex. Having 3 Sorcs in D2 to have one of each element). I think 10 is way more than enough since I don't think people will play more than 5 unless they want to level again, play in hardcore, or something of that nature. I'm actually surprised Blizzard gave us that many slots to be completely honest.
I don't think that it will specifically be a Druid but I can see a shapeshifter of some kind in future. I mean this as it will be a mainly physical damage and melee character presumably and not have any nature magic (besides maybe some auras?). I'm not sure either what forms would work out with the lore and such but I was always a fan of the Werewolf form and think it would be a great addition to the world. However, I do know that the whole Werewolf thing is cliche and many fantasy roleplayers seem to have a hatred towards anything werewolf, vampire, or dragon in combination with shifting.