Extending Application to external users

We have an ERP system developed in CUBA platform, want to build options for external users like Customers, Vendors who will be able to use a limited transaction/view e.g. view account statements, log claims and disputes etc.

There could be two alternative scenarios in terms of the number of users:

  1. A limited number of users e.g. few hundreds to a couple of thousands of concurrent use
  2. The number is unknown, as this could be public

Under the cases which technology do you suggest for scenario 1 and 2 respectively?

  1. Do you suggest the same generic UI for scenario 1?
  2. For scenario 2, one of the options could be Portal development. I see it is not much covered within CUBA platform; In such a case, what do you suggest as technologies, IDE etc.?

I would appreciate the guidance and expert suggestions.