Accounting inside SuiteCrm

  1. Yes, by modifying the existing products module. Check details here (Inventory Module)
  2. If you want to use inside CRM, needs custom module to be developed. (can do via studio)
    1. Same as 2
  3. Check how Web to Lead works. Wordpress does provide hooks which posts content to any other URL for notification or processing.
  4. I would suggest just keep payment records and do the payments on the vendors site. Just a link to connect to their site.
  5. Use workflows to create alerts, otherwise a dashlet with status filter is enough.