Can install theme while migrating data ?

Hi there,
Please proceed with data migration and verify all migrated data ready for use. Then you can start with theme and extension integration. 
This is the best workflow to avoid unexpected issues due to the migration process.
Regards,
Ubertheme team

Hi there, 
When proceeding with the data migration, you can either connect directly to your live Magento 1 db (our migration tool just read only and does not make any changes to your M1 db) or use the option below: 

• Step 1: Create a new database for Magento 1
• Step 2: Create a dump of Magento 1’s database from your live database, 
• Step 3: Import the dump file to the Magento 1 database, which you have just created.
• Step 4: Navigate to your our tool dashboard in your Magento 2 instance, fill in Magento 1 db credentials that you’ve just created.

Hope that helps. 
PS. Our apology for certain delay in response if you reach out to us during the weekend. 
Regards,
Ubertheme team