I'll start with 2): Yes, currently, PREMIS rights statements are still not visible to public users. If you have applied rights-based restrictions to your digital objects, then instead of displaying the digital object, AtoM can display a custom access statement, which can be configured for each rights basis in Admin > Settings > Permissions. See:
The PREMIS rights module isn't very end-user friendly for researchers who are not familiar with PREMIS or the various ways in which an institution might internally describe the rights and limitations associated with a particular record. Since donor agreements are also a possible basis for a restriction, there are also use cases where users might want to record information internally with more detail than they would want to make publicly visible.
For capturing public information on access and use, we recommend using the elements within the content standard itself, such as Conditions of access and use and other related fields. An additional advantage to this is that since the metadata is a part of the description itself, it will be included in description exports as well, while PREMIS rights statements are not currently part of the archival description import/export templates.
RE: 1): There is not currently any way to create a default, reusable Rights statement - though this is an interesting proposition! You're right that in AtoM's data model, rights are their own entity, but we also don't have a way to create a default archival description, authority record, repository record, etc. We have had some interest in this come up before - the ability to predefine some fields that are going to be the same for many records so that you can "quick add" new records and only need to make a few modifications (like title and identifier) - but so far, no one has sponsored development for this. Since it would involve a lot of new page types, settings, and database changes, I would imagine it to be a fairly large development project, but it should technically be possible to achieve!
Unfortunately, for now this means you will need to keep creating your rights statements manually.