How to structure WordPress

I’m building an online community. I would like to use the “Stained Glass” theme on the main part of the site that includes a landing page and other pages with info about our company. I want users to then be able to login or new users to be able to register from that main page, which will then take them into the community itself(buddyboss theme). I have installed WordPress manually at the root, buddypress, and the buddyboss theme and child theme as well as several plugins. I also want some of the profile info(from buddyboss) able to be displayed on the mainpage(stained glass theme) like most viewed profiles or other metrics.

I’ve tried the multiple themes plugin to accomplish this with no success. What is the best way to do this? Do I have to use multi-site? Is it possible to accomplish this with subdomains and directories? I’m new to WordPress development and have just scratched the surface to start getting educated.

I need help on how this should be structured and where to get the education to solve this. Thanks in advance!