Point 1 is probably your issue.
BuddyPress does not work on installations where you give WordPress its own directory.
To resume a default BP install.
your-site.com is the root. Generally a folder called htdocs or www. Once WP is installed you have something like this:
serveur/path/www/wp-admin
server/path/www/wp-content
server/path/www/wp-includes
BuddyPress goes to /server/path/www/wp-content/plugins/buddypress/
This will not work if you use BP /server/path/www/mysite/wp-content/plugins/buddypress/
