Softpress Managed WordPress, is it possible?

You can use Softaculous to install WordPress, set the username and password of the administrator.

There is only one add-on that can be selected when installing Softaculous (Limit login attempts).

Regarding the themes, the Softaculous installer allows you to choose some, but you could not limit the topics. Users can simply upload a theme through their WP administration area unless they have made changes to avoid them. I'm not sure if Softaculous could help here in any way.

You can always contact Softaculous, can you have an option or two available for you: https://www.softaculous.com/support/open.php?