Hey Alysia,
For No.1, yes you are able to add Custom Profile Fields, you would just need to install the plugin, create your custom fields in the plugin options page, and add the custom field display to the theme template.
No.2, yes – you have the option for admins to receive email notifications for new posts which can be set up per admin, and using this alongside the Admin Bar plugin will allow the posts to be easily singled out for admins to view, mark as read or remove. If you want to be specific, you can also have an admin subscribe to an entire forum which will also give an email notification on new posts.
And No.3, not quite clear on what you are asking here. The forum sits on one WP page dynamically, and I am not sure you can have more than one install of SP on your WP site, however we do have a large handful of users (possibly more) that successfully run multisite installs, although I’ve never done this so can’t really comment further on that one!.
If I am off the mark on that last one, please elaborate on what you are asking there..
Hope that helps.