Hi Wen Hao, very interesting investigations that you are carrying out here. At Catalyst we are familiar with a number of solutions to e-commerce for Totara. These can range in function and complexity from a  simple plugin enabling course charging to a robust hybrid systems using Drupal, Magento or other E-Commerce front ends. In particular, the e-commerce Totara LMS platforms built with a CMS 'front end' such as Drupal will support many of the integrations that you require with readily available community plugins. Whilst the building of the hybrid environment will of course take time and careful consideration, we have seen great success with this solution.

The simpler option outlined above may be to use a service such as Course Merchant which does include a Moodle plugin that would probably be suitable for use on Totara. However, we have not tested this to date.

I am happy to share a discussion if you  wish to further understand what you are seeking to achieve.

Kind regards,

Joey