It's all how you want to do that, you can start with admins and then you will know should you allow other users as well or not.

Polls can be created only with Topics, there is no other place to create them.

If you want to create a poll, you have to Press on Add Topic button and then on Create Poll button. There i no other options, Only that one.

About who can create polls. That is related to the Forum Accesses, after installing wpForo Polls addon, in the Forum Access option you will have these 3 options:

• Can create poll
• Can vote poll
• Can view poll result

And by the Forum Accesses, you can choose which usergroup Users in which Forums can work with Polls.

1) can the admin create the polls in the admin backend?

2) Can the polls have a comment form so people can discuss the polls in the forum, I think it does this as think I read when creating the poll, it also creates a forum topic so people can discuss the poll, is that correct?

For creating a Poll, you need to create a Topic. So you do the same as creating a Topic and before publishing the topic you press Create poll in the topic field, setup it and Publish the Topic with the Poll.

There isn't any option for creating the poll from the Dashboard.

3) I am currently building the site on a test domain first, when it goes live can the plugin work on the new live domain instead of the test one, could it be transferred over or would I need to the licence for 3 sites or could I just get the licence for 1 site and just transfer the licence from the test domain to the live domain?

Check this Topic, there you will find the needed answers: https://gvectors.com/forum/product-license-questions/license-activation-on-development-website/