Yes to all questions.

Before rolling for any units you must nominate which unit each character that is required to join a unit is going to be deployed with and then roll once to determine if they all turn up or all are delayed. For example a Skaven army with a Grey Seer on a Screaming Bell is playing against an Orc & Goblin army with Skarsnik. The Grey Seer would have to nominate which unit of Clanrats or Stormvermin he is joining before any rolls are made to see which units are delayed by Skarsnik.

No, once the Wizard has left the unit it will only target him. If he subsequently joins another unit, or rejoins the unit he has left, while the spell is still in play then they will benefit from the spell.

Yes, as long as they end up in the rank closest to the front of the unit that has a space in. It is also worth remembering that even if only the character moves the whole unit will count as moving that turn. Having a belligerent officer barge his way through the unit is not conducive to a good round of shooting!

Yes.

Yes.

Yes, but for that move only.

As soon as the last model from the unit has been removed, any remaining characters will count as a new unit. Note that this will cause Panic tests to all friendly units within 6" (including the newly formed unit of character(s)) as the unit has been destroyed.

No.

If the challenged model is on his own then he must move into base contact. If the challenged model is in a unit he must move as long as it does not require leaving his unit. Where it is not possible for base contact to be made then leave the models where they are and simply assume that the two models are in base contact.

Complete the challenge as normal this turn. The model which has ceased to be a character must use its non- character (and thus probably much reduced) stat-line from the moment the spell ends. At the end of the round of close combat the challenge automatically ends.

No.

Yes.

No.

Yes. Additionally, if there are multiple riders they can each shoots

No.

Yes.

Yes.

Yes.