Hobby is fine, as anything above is only needed to deploy to live.

Yes, and make sure to delete all existing data structure you may have in your existing application associated with Blog as most data types may be same name which causes issues as Bubble doesn’t change the ID for the datatype on their end when you simply change the name of it. Then after deleting your existing data types, use the optimize app feature to really remove them. After that you can just copy and paste the data structure from the template and add any necessary fields for User data type that may be necessary.

Performance of SEO is something that has a lot of factors, many of which are completely out of the control of the application itself. The only thing the template does to help your SEO performance is to give you ALL of the on page SEO features/functions.

Below is screen shot from description on the public page for the template of the features included to help your SEO.