Email templates access
There's no built in support for that, and you'd have to make a number of edits to the CMSB code to enable it, which would make it so you couldn't upgrade the software without overwriting those edits, and potentially allow users who can edit email templates to break the system by erasing or modifying templates and/or send or trigger spam being sent (by editing templates and requesting password resets).
We actually have a few clients who edit their own email templates, and they do get broken pretty frequently.
So I'd recommend either giving them full admin access and tell them to be really careful because it's easy to break things and fixing broken things is billable time. Or if you want to hack the code to allow it I can tell you how to do that but you'll probably want to let your client know that would mean more time required to recreate those edits when they want/need to upgrade the CMS.
Hope that helps!