I want to have a Human Fighter / Druid, starting with about 9 Fighter levels and after that switching to a Druid. Seems better than a Paladin IMHO.

I don't find the Stats requirement for Dualclass Druids in the Manual, what do I need to have?

Strength 16 for being a fighter and Wisdom 17 or Charisma 17 or both for becoming a Druid?

You need 15 in the Prime Requisite of the original class, and 17 in Prime Requsities of the new class. For Fighters the PR is Strength, for Druids it seems to be Charisma (the manual doesn't specify the Druids' PR, only that charisma is important for them).

Wisdom and Charisma are both prime requisites for a Druid. Wisdom is the more important stat for priest spells.

You need a true neutral human with 15+ strength, 17+ wisdom and 17+ charisma.

Is 17+ Charisma of any practical use (execept for Conversation which are kinda unimportant in Icewind Dale)?

Can I impress the ladies with that?
I guess not...

Just like in Baldur's Gate, high charisma will get you some discount at shops when buying equipment, but only if your charismatic character is the party leader.

The Wisdom only needs to be 15+, oddly.

Thank you very much, my fighter druid will soon join the fray...

Icewind Dale uses AD&D rules. In AD&D, druids must be of true neutral alignment, there are no exceptions. Icewind Dale II is a different story.

Unless using the component from Dale Tweaks "Druids Use 3e Alignment Restrictions."