I've never been to ITB so I can't give you any immediate advice, but you should be warned that the ground staff at TXL and SXF are likely to begin an indefinite strike on Friday. Further details are expected to emerge tonight. Their union has announced that it will give 12 hours' notice.

Of course, the airlines won't cancel any flights before the union officially announces their strike, which is rather unfortunate for people who are hoping to travel through TXL on Friday morning (such as me) and wouldn't mind being able to arrange alternatives if necessary.