Which is the best detail to add to support opening a new
library?

The best detail to add is something that can persuade people, in order to not only attract them to the library, but to tell them that you know what you're doing.

For example, here are some questions to ask yourself that might help you:

If I opened my own library, what would I do in order to make it popular?

What types of books are best selling, so that people come in and buy them?

What can I do in order to make the library stand out?

Then from those questions, turn them into statements that can be details to help support opening a library.

Here is an example:

Supporting a newly opened library wouldn't be a bad idea, because it may have new, and best selling books!

A new library should be opened in order to appeal to other's eyes, and stand out! I think that would be great! It would be knolegdable and appealing!

scholarship is an sc because, by definition, a subject complement is the adjective, noun or pronoun that follows a linking verb, for example the verb be (in any of its forms).