Sorry to reply a bit late and luring you to this Mad house, laddie. Anyway welcome to SYM
I just finish the whole W3 : FT today - yea, took me a while with my current RL state. The game is fine not good though.
As for storyline I see some Starcraft influence in it. We all know that W3 have that Starcraft influence on the unit & building side but now it gone worse

If you check out BattleNet forum you'll see other complaint about this matter too.
The Human Secret Bonus level is great - for those who dunno about it ya gotta look harder. It can be accessed via stage where Prince Kael was rescued by Lady Vash (IIRC that's the spelling).
The Orcs does not have anything to do with WC3 : FT. But you got nice Bonus campaign which according to Blizard & their forum news will be continued and avaliable to DL sometime in the future.
Back to the storyline :
1. Illidan death or not is still uncertain. Blizzard can make you think he's dead (since Arthas slice him on the finale and left him lying bleeding) but I suspect another loose end which will be used by Blizzard sometime in the future (we still got no idea how he manage to get the Nagas, only he was ordered by Kil'Jaeden. And we dunno + ahve not seens who's the Queen refer by Lady Vash in most of her acknowledegement voice)
2. & 3. It's probable that Sylvanas will face Kel Thuzad in next game. After all Kel did promise Arthas to look after Lorderaeon. How and what happen ? it's all up to Blizzard.
Then again I really really hope W3 future story will not turn into another Starcraft influenced saga
