Caroline,
Thanks.
1. All blogs created until the content freeze will be migrated.
2. The blog tile will link to the LA instance, eg:
http://blogs.glowscotland.org.uk/nl for North Lanarkshire
There will be links there to: My Blogs where users will see their blogs and a link to create a new blog. In phase 1 this home page will be very simple but will have more functionality in phase 3

More questions, keep them coming.