I want to slide a vertex only until it perfectly reaches the height of another desired vertex, this saving the time of having to create a vertex at the edge intersection. The problem is, I have no idea how to do this or even if it’s possible. Isn’t there some kind of smart guides blender can use like photoshop has?
Just use vertex snapping while you move the vert. You can constrain it to an axis to keep it in line:
I dont think you can slide a vertex to have it snap, but here are a couple tools and tips you can use:
Scale to active select:
https://gyazo.com/8d4055f011a9b8f0889d1d93ce367b3dEnable 
Active select, then use this to scale by 0
https://gyazo.com/aa265b9468b18b6ad378ac74a50a60cd
Vertex snap mode. then initiate the Translate tool (move tool), hold down CTRL, and hover over a vertex.
https://gyazo.com/d391ff46e2fe2398a8e23d1809562a5d
CTRL+Alt+Space will lock the gismo to current selected “normal”.
This can also be used to straighten verteses between any two points:
https://gyazo.com/f472b71984cd660d5240a6a5fd24c6d3