1) Currently the only payment option is Paypal. If you want to implement offline payments you can make a regular page for offline payment instructions and add link to that page on sidebar or before/after ad listing on ad page.
2) Classibase script works on web hosting with PHP/Mysql with local storage, preferably on linux web server. I am not sure how they are enabled on amazon web hosting. Found some instructions about it here but we have not tried any of those.