Question 1 - We have a subscription membership site on WP and want to ensure that our wpForo forums are only available to our site members. Is there was way to do this.

It should be set by your Membership plugin, you can edit the main forum page and set according options. i dont know exactly how your plugin restricts access to any page.

Question 2 - Is there a way to allow members to start their own forums on topics that are important to them?

Users can create own Topics in Forums. Forums are the categories of topics not vice versa. Please read the documentation: https://wpforo.com/docs/root/topics-posts/new-topic-question/

Question 1 - We have a subscription membership site on WP and want to ensure that our wpForo forums are only available to our site members. Is there was way to do this. 

Question 2 - Is there a way to allow members to start their own forums on topics that are important to them?

Thank you for your help.