Hi,
Easy Profile extends Joomla user management (not replace), so edit profile/registration forms are the same of Joomla (tabs are generated via Javascript and Custom Fields added with standard user plugin).

You can use all Users Plugins with Easy Profile.

To get/set Easy Profile fields you can use our API, see docs at http://docs.easy-profile.com/index.php/article/jsnuser-object

Unfortunately we have no experience with RSForm and EB Event.

EasyProfile compatible with RSForm

What do you mean by compatible? I know that some our customer use Easy Profile with RSForm, try to search in this forum.

Hi,

So my question is: how can I create a form with all the fields I need, if I decided to opt for EasyProfile?

if you want use RSForm to register users and fill Easy Profile data from this form then I think this integration need to be developed by RSForm Team. As we have said we not have experience with RSForm.

it looks to me that it can only use the very limited native Joomla user registration form

This is the best feature of Easy Profile, no second user management tool, all perfectly integrated with Joomla user management.
Anyway, Joomla user registration form is very powerful, it uses JForm Joomla API, so with user plugins you can customize your form what you want. I think that replacing the registration form is a workaround or a way for multipurpose component like RSForm to integrated this. Still, using Joomla registration forms allow you to use users plugins developed by third-party developers. The concept is that Joomla User management is a part of Joomla and it should centralize all data from all components (there are Joomla API for this).