Deadpool isn't a part of the Infinity War comic. The Infinity War mainly focuses on a specific set of characters, and Deadpool doesn't fit into that narrative framework.
Sure. Some Deadpool comics incorporate the Infinity Gauntlet, creating wild and unpredictable storylines that blend Deadpool's crazy antics with the cosmic power of the gauntlet.
In this type of fanfic, the Infinity Stones could have a very different effect in the Harry Potter universe. For example, the Time Stone could be used to reverse dark spells or resurrect fallen wizards. However, the Stones' power might also be limited by the magic rules of the wizarding world. The fanfic could delve into how the characters from both universes adapt to the presence of the Stones and how they use or misuse their power.
Definitely. The Infinity Gauntlet comics came out earlier and laid the foundation for the concepts and characters seen in Infinity War. There are some differences, but the comics serve as a precursor.