I have a migration which creates several records along with the table. eg Forum.create :title => "General Discussion", :description => "General Chit-Chat"
I am not sure you want to combine migrations with record creation. It is probably best for you to handle this via a load script or a rake task.
As to the file upload, if you are using a plugin like attachment_fu, then you are all set. Take a look at the plugin tests directory to see how those simulate the upload of files and create the uploaded files either in the db or in the path you specified in your models.
