Moving to Vienna from London

Hi,
I'm new to this group, thus unsure whether I'm posting this to the right group or whether it has not been discussed previously.
I and the kids are planning to move to Vienna early next year. We currently live in London and my husband would temporarily stay working there.
Can anyone advise what paperwork we need to sort out, mainly from the British side? Any help/advice would be much appreciated.
So far, we are aware that we need to get E109 form from the UK (to be entitled for the social insurance in Austria), anything else?
We would also need to register my son for the nursery, for which once again one needs a social security number (and living in the same district?).
Does anyone else have a similar experience?
Thank you in advance for all your help.