Content protection of posts using more tag

Sorry for the basic question but I'm new to all of this and a bit overwhelmed building out my site right now!

Regarding use of the more tag. I want "visitors" to be able to see the posts but be directed to a restricted page when they click on "read more". My question is, do we need to insert the "more" tag into every single post or can we take advantage of the WP default functionality where after x number of characters a "read more" link is automatically inserted into the post? I am able to get the more tag functionality to work but am hoping there is an easier way to automate this.

Thanks!

-Dave