Subscriber list clarification

I have migrated my Wordpress.com site to Wordpress.org and am now working to set up Convertkit (Kit) to start a newsletter.

Kit allows moving my 73 subscribers from WP.com over, but it does caution not to do so if these people have not given permission to receive the emails from me/Kit.

My question is, since my WP.com did not use double opt-in, and this is a list of people who only clicked “Subscribe,” is it OK to import this and introduce these subscribers to the newsletter?

Or would it be better to start with no subscribers and do a blog post announcing the newsletter with a chance to opt-in?