Migration of content with an UI
The Wordpress Migrate module is a great example of how to implement a UI to upload a file and create a migration for it. Once you have that, it shouldn't be too difficult to run the actual migration via code.

Create Migration configuration from information and file provided to your Wizard Form. Then the following should work.

$migration = Migration::create($configuration);
$executable = new MigrateExecutable($migration, new MigrateMessage());
$executable-&gt;import();