Suggestions for planning project tasks and organizing classes/functionality?

I am curious about "Best" practices for organizing things within unity and keeping track of tasks and subtasks for your project.

This includes things in the hierarchy, assets folder, inspector, classes, variables, etc.

I want to eventually use git as a history, but I am the sole developer, and don't see much use for it.

One of my classes (RTSUnit) has a ton of code and methods for handling aspects of an RTS Unit in my game. Is there a way to break up functionality, such as commands that can be given, the current command, weapons the unit has (and their Vector3 mount points in relation to local space), stats of the unit, and other aspects?

My idea was to create this class, and then customize properties for each unit type I want by subclassing from this, and then setting values in Start(). I want to avoid inspector changes, because I've been burned in the past with a bug in Unity, where my inspector for prefabs would reset to default. Plus portability in case of needing to upgrade and look at code to determine the state of a particular unit type, is preferred for moving forward in the future.

I have a decent number of tasks I want to do, each with subtasks, and currently I just work on one at a time, but I want to eventually have a nice way to organize this so I know what needs to be done, and what is currently being worked on. Any ideas on this?

Because of the nature of my code, I want a nice way to plan out future additions, and where each change or variable / functionality will eventually lie in my code. I considered UML, but I am unsure of a good program that can support comments and easy viewing for planning out my classes. Any suggestions?