No, you just need to add in additional code for the additional field. In most cases by just duplicating the existing code, e.g.
add_preloaded_topic_list_custom_field(FIELD_NAME_1)
add_preloaded_topic_list_custom_field(FIELD_NAME_2)
The first place to look for custom user fields is /admin/customize/user_fields which gives you a UI to add them. If you want to have more granular control, the process looks very similar to topic and category, but you don’t actually need the frontend elements with user fields.
Actually we’re (Pavilion) thinking of making a custom fields plugin (analgous to ACF for wordpress) which would initially look a bit like the custom fields admin interface in the Custom Wizard plugin.
Actually, some people already use the Custom Wizard plugin as a custom field manager. It lists all custom fields on your instance (from any source) and lets you add a field of any type to any model that supports them.
It doesn’t add in frontend support, e.g. like that show in the Topic Custom Field educational plugin (and that wouldn’t work in the context of the custom wizard plugin), which is why we’re thinking of breaking that out into a seperate plugin.