Who will chair the first sitting? 

The sitting at which a new President is elected will be chaired by the outgoing President or, if that is not possible, by one of the outgoing Vice-Presidents (to be determined according to their order of precedence), or, in the absence of any of them, by the Member who has held office for the longest period.

The European Parliament elects its President from among its Members.

Rule 14 : Provisional Chair

1. At the sitting provided for under Rule 146, and at any other sitting held for the purpose of electing the President and the Bureau, the outgoing President or, failing him or her, one of the outgoing Vice-Presidents, determined in accordance with their order of precedence, or, in the absence of any of them, the Member having held office for the longest period shall take the chair until the President has been elected.
2. No business shall be transacted while a Member is provisionally in the chair by virtue of paragraph 1 unless it concerns the election of the President or the verification of credentials under the second subparagraph of Rule 3. Any other matter relating to the verification of credentials raised when he or she is in the chair shall be referred to the committee responsible.