The sideview fighting is a script from Jet and the combat is a mix of a lot of scripts from Yanfly (And a lot of time put in to set them up and tweak the scripts as needed).
The fishing, though - that's done completely with events. I'd recommend looking up tutorials and just a lot of playing around with the program. Once you've got a grasp on everything that can be done with eventing, you can then think about possible ways to use that knowledge to do what you have in mind.
I learned by playing around, lots of trial and error. Also there are forums you can post on to ask for help if you run into any problems.