No. It is not an appropriate area to explore as it contains elements that are not suitable for public consumption and can make many people uncomfortable.
In a sense, it's not a literal 'watching' as the show is an inanimate creation. But in the context of the show's creators or those associated with it being aware of fanfiction, it can be normal. They might look at it for inspiration or to gauge fan interest.
The main difference is the macrophilia element. Regular Supernatural fanfiction usually sticks to the themes and storylines within the show's framework more closely, like hunting monsters and the relationship between the Winchester brothers. But Supernatural macrophilia fanfiction adds the macrophilia concept, which changes the focus and can lead to very different character interactions and plot developments.
Well, Tumblr can be a great place to search for Supernatural fanfiction. Many fans post links to their favorite fics or even write short ones directly on their blogs. Another option is Wattpad, though the quality can vary more there. Just search for 'Supernatural' in the search bar, and you'll get a bunch of results.
It could imply that the show 'Supernatural' in some way is associated with or has an influence on the fanfiction related to it. Maybe the show's creators or actors are aware of the fanfiction and are 'watching' in the sense of being aware of what the fans are creating in that realm.
Well, in fanfiction related to 'Supernatural', some writers might show their acknowledgement in various ways. For example, they could reference the original show's plotlines and characters in a respectful manner. This can be as simple as using the correct character traits and backstories. It shows that they are aware of the source material and are building on it in their own creative way.
I'm not sure which one is the absolute longest Supernatural fanfiction as there are so many out there. However, you can try searching on large fanfiction platforms like Archive of Our Own. They have a vast collection of Supernatural fanfics and might give you an idea about the really long ones.
There might be a fanfiction where Sam and Dean Winchester find themselves in a town during the purge and have to figure out a way to stop a powerful supernatural being that is taking advantage of the lawless night. They could team up with some local survivors who have some knowledge of the supernatural.
Azrael in 'Supernatural' fanfiction is often depicted as an angel of death. In the context of the show and related fanfictions, Azrael has powers related to death and the afterlife. They are usually a very powerful and mysterious character.