BuddyPress.org

For help re IIS setups, you’re better off asking elsewhere.

Re WP / BP: Have you done some basic debugging ? To narrow things down ?

Try this: wipe the WP and BP installs.
Start over.
Do not use the Alliance theme initially.
Instead use a WP theme like 2016.
Don’t install or activate any other plugins.
Create a few users manually.
You may have to create the BP pages manually. And then manually assign them to BP via .../wp-admin/admin.php?page=bp-page-settings.