Hi,
1. You can set price based on usergroups, so no price for guests, only price for registered, then a small translation override is required, or as you said a view override.
2. Can be done with the previous restrictions
3. Via the menu Display > Custom fields, you can add such kind of custom field in the user table.
4. That should already be happening, are you receiving the Joomla emails ? like the one for the registration or another ? We use the Joomla email system, so if you don't receive them, that's potentially because of your settings in Joomla or server.
5. This is more a Joomla issue than a HikaShop one.
hikashop.com/extensions/compare-versions.html
Regards,