First thing about the plan is that WordPress is a CMS - a Content Management System, it is sort of self contained. You set the URL for it when you set it up, then it creates its own URLs based on the Permalink structure you set up. The internal URL structure is handled by the settings. Installing multiple installs of WP on one domain 'can' be done, but there are other versions of WP that you might want to consider when you reach the point of expansion. If the concern is the URL structure, you control that in your Admin > Settings panel, not via rewrites.
It is a good idea to set up a plan, think about what you want to do and then decide what will work best for you. It is a good plan to learn how the CMS works before you get big and busy. Not a good plan to learn as you go and try to make it do things it doesn't do well. An example is the /subscribe issue - that is best handled using plugins rather than "pages". It may take a few weeks (or more) to research your options, but it is better than trying to patch it together with .htaccess rewrites.
A problem of running a WP install from a subdirectory and having it appear to be in the root directory is that it requires an index.php file to stay in the root directory so installing a separate WP install in the root directory would be very tricky because there are then two index.php files in the root directory (there can only be one). In that case you probably want
WP MultiSite [codex.wordpress.org]
My recommendation is that you first set up a
single WP install [codex.wordpress.org] and learn to deal with its ways, then if you need to expand you can always move that database to a different version.
Something to keep in mind while you are researching is Security. Because there are so many WP sites, it is a popular target for exploit attempts. Spend time learning how to strengthen your install before it is loaded up with data. Also remember that Plugins are not magic. Research them well and use sparingly.