How to see which functions are being called the most?

Is there a way to know which functions i wrote are being called most? (aside from update ofc)

 

Yes, that's what the Profiler does for you.

 

Does assets that are on the project but not used count up when building? I.e, do you have to find & delete unused assets before building or does Unity discard those for you?

 

Unity will ignore unused assets when building the project unless they're in a folder named Resources. It's possible to have multiple Resources folders too so if you add third party assets to your project you may need to check to see if any of them add folders with that name.

https://docs.unity3d.com/Manual/SpecialFolders.html
https://unity3d.com/learn/tutorials/topics/best-practices/resources-folder

 

Use the profiler. In many cases, Update isn't your culprit.