The DB user would definitely need to have the ability to do CRUD operations on tables and have the ability to create, drop, and alter tables.

They would at least in the very beginning (and any kind of upgrade work afterwards) need to have the ability to create and drop schemas, especially if custom modules are being added in.

And as you pointed out, it would need to install the CLR functions and create the DB in the very beginning.

Beyond this, I don't think there's anything else that would be needed here.