Commercial Door / Metal Door

I asked this in another thread but didn't receive a response, so I figure I'll ask it here in the proper forum.

Is there any difference between the Commercial Door and the Metal Door library parts in AC11?

Is there a way to get a mullion in between the double doors?

I never realized there was so much to consider when it comes to fire safety in buildings. Especially the part about hollow metal doors (https://www.usafiredoor.com/commercial-doors/commercial-steel-doors/hollow-metal-doors/) – seems like they're not all created equal.

Is it fair to say that when it comes to fire safety, it's always best to err on the side of caution and go with the most fire-resistant option available?

For someone like me starting from scratch, are there any resources or online communities you recommend for getting a better understanding of fire door regulations? The more I know, the better I can sleep at night!