Hi @alnstark777, welcome to the Sonos Community!
Our Soundbars, the Sonos Arc, Beam, and Ray, can only be used as front channel speakers (or the main speaker if you want to call it that) while the Amp can be used for either the front channels or the rear channels. Since you’re using the Beam Gen 2 already, then you can bond the Amp with it to act as the rear surrounds.
Since you’re connecting the Amp as surrounds you wont be able to connect a third-party subwoofer as that is only available when being used as front speakers. Without replacing your Beam, you can connect a Sonos Sub or Sub-Mini to act as the subwoofer.
Connecting two passive speakers is fine, as well as four if you want, but I don’t think more than two is necessary if you’re using it as rear surrounds.
Your last question seems to be a repeat of your first one, I assume you’re asking if you can connect the Beam to the Amp and have the Beam act the surrounds, which isn’t possible. If I was wrong and you meant something else please let me know. I hope this information helps however and let me know if you have any further questions!