Is there any way to either:
In reference to option 2, it doesn't look like it will let me select anything as a default. I think this is because the Blueprint lookup is a dynamic query lookup - can you please confirm?
The default for blueprint attribute can't be set in Studio and that is by design.
With that said the default blueprint can be set in MUX->Administration->Blueprints by right clicking on your desired blueprint and set it as default.
There are 2 blueprint related attributes: Blueprint and Blueprint Active ID.
There are different ways that projects or ideas can be created, for example by clicking on the Plus (+) sign in MUX, right click on instance and do copy or creating from Template. When creating from template it is taking blueprint from template but when creating using plus sign it is assigning it to the default blueprint you set, yes you don't see it populated under Blueprint attribute but if you check the Blueprint Active ID you will see the value of the default blueprint and that means your default blueprint is taking affect.