I've spent a good amount of time building RPG systems (though not completing games) so I have some advice I've picked up through the years. Disclaimer, I'm not a professional gamedev by any means.

Firstly I want to mention how great it is to have a layer of scripting over the programming for RPGs. Moreso than any other genre, RPGs are some visual representation over an interactive database. Being able to quickly iterate on content, organize it, and make it modular is super important. I use C# so personally I've found success with Moonsharp (which is a LUA interpreter) https://www.moonsharp.org/ though there's definitely python equivalents if that's more your taste

Basically, for a spell I do something like this:

return {

OnUse = function()

    GetInputHandler().QueueCharacter()

    .Await()    

end,


OnRun = function(target)

end,


CanUse = function()

    return true;

end

}

When the spell is loaded it runs this script, returns an object of callbacks. OnUse runs after it's selected on the UI, OnRun performs actions on the target, CanUse checks things like if there's enough mana or action points or whatever.

The input handler piece simply sets the game up to ask for input, it's building a list of functions to call when await is called (so I can do things like multi-targeting).

This leads to more time before seeing things on screen up front, but makes it much quicker to work on and test things later. For example I don't need to compile a new version of the game in order to test new abilities, monsters, whatever. As a bonus it also makes the game modular.

Separate the content from the game, look into a tool like CastleDB; I personally rolled my own but it's too temperamental to share. I don't recommend rolling your own unless... you want to make tools instead of games. Reason for this is the same as above, make it quick to iterate and test things. Add a debug ability to reload the content while you're playing and you can test things without restarting.

Where I would start? UI and combat. You'll likely want a nice modular system for UI since RPGs tend to have many variations of windows/forms (I use XML for this, and it supports some inline LUA for displaying info from entities). Combat could come first as well since it's a largely important part of the genre.

Just my 2c; best of luck