HOW TO MAKE A NEW CHAPTER FROM SCRATCH:
    Step 1 - Go to Chapter_Data.xml and copy paste one of the existing items, all the way from <Item> to </Item>. The key is basically the key phrase you want associated with your chapters' files, so make it an abbreviation of the chapter's name or something. The Turn_Themes section determines which music plays during each team's phase, same with Battle_Themes. Next you determine the Text Key and the ID's of Map, Unit, and Event data. You can just go with Event data and ignore the other two, or vice versa. This essentially determines what files the game will load when you start the chapter. It'll either load up an event, which will start loading up the other components (map, unit data), or you can just have it load up the map and unit data directly with events being bypassed entirely. You'll want to have a text key regardless. Bear in mind that the name you specify for Event Data has to be the EXACT name you are using for the event itself, so you don't want to just call it 'Chapter1' or 'Ch1'. Call it 'Chapter1Intro' or 'Ch1Intro' instead, to make it easier to tell which event is which. The event you're specifying here isn't really the MAIN event, it's just the first one that will be loaded.

    Step 2 - Go to Config.cs and scroll down to where it says:
    'public readonly static List<World_Map_Chapter> CHAPTERS = new List<World_Map_Chapter> {'
    Here you should see multiple entries for all of the currently selectable chapters. As above, simply create a copy of an existing entry and edit all the specifics to your liking. Most of the criteria are pretty self-explanatory except for Loc, which I THINK determines where the world map will scroll to when you select the chapter.

    Step 3 - Make a map in the map editor. Bear in mind that only some of the tilesets have been fully coded into FEXNA yet, so for the sake of simplicity, I suggest you just use the Fields tileset for now. Once you've made the map, import it into FEXNA - DO NOT DO THIS BY COPY AND PASTING THE FILE. Instead, with Visual Studio open, navigate in the sidebar to where the .map files are kept, and DRAG your new map file into that folder within Visual Studio. You'll want to do this with basically all newly added files, otherwise the program will not know that it is supposed to be working with this new file. Once it's imported, open it up in Visual Studio for editing. You need to change the first line (which should be the name of the tileset) to the ID of the tileset you used to create the map. For Fields, this ID is 0.

    Step 4 - Make an Intro event. You can bypass this step if you only specified Unit Data and Map Data in Chapter_Data.xml, as the game will not bother loading it. Now, you can get what you need here simply by making a copy of Tr1Intro and then deleting all the unnecessary events, but if you want to start from scratch, make a new event called [Key]Intro. So if your chapter's Key is 'Ch1', name the event 'Ch1Intro', etc. Add an event group inside your Intro event called 'Startup'. Now add the following events:

    Chapter Change Effect
    Change Chapter
    You can add tons more than this, but I believe these two are the bare minimum you need for this to function.

    Other suggested events are:
    Heal Actors
    Change Screen Tone
    and:
    If statement : HardMode
    Change Chapter (hard version)
    Else statement:
    Change Chapter (normal version)
    EndIf statement:

    The Change Chapter event is a bit tricky, but it's pretty easy to understand. The box on the bottom right with the grey text is a guideline. It's showing you what you need to put on each line. On the first line, write 'false'. On the second line, write 'true'. On the third line, write the name of your Chapter (which should also be the name of your .map file). On the fourth line, write the name of your Chapter again (which should also be the name of your unit data file). On the fifth line, you can either write 'null', if you don't have any further events coded for your chapter, in which case the game will not load any more events and will simply let the chapter play out normally, OR you can once again write the name of your Chapter, which will tell the game to load an event by the same name. Consider that event the main event, as it will contain most of the chapter's configuration (village events, talk events, manual inventory and unit management, cutscenes, scripted battles, etc etc etc.)
    Once you're done with all that, add your Intro event (and any other events you may have made) to FEXNA in the same way you added your map file.

    Step 5 - I am not sure if this step is required, but you may as well do it anyway as it requires very little effort and will be useful later. Simply open up the Text Editor, make a new entry for your chapter, then save and import the new file into FEXNA in the same way you added your Intro event and .map file. This is just to avoid the game saying 'wait where is your text file', even if you have no text events currently coded into your chapter. Later on, when you're fleshing this chapter out, your text file will be where you write ALL the dialogue that takes place during the chapter. When importing this file, make sure you put it in Data > Text.

    Step 6 - Start debugging (playtesting). Once the game starts, press Z, X, Shift and Enter simultaneously. The game should now restart back to its main menu screen, which is usually skipped when you start debugging. You'll also notice some new options on the menu, as this is essentially the in-game debug menu. At the very bottom, you'll see 'edit map units'. Click that, then select your newly added chapter on the world map. Your newly created .map file should be loaded, and you are now free to go around placing units wherever you like! The controls for this are pretty similar to the actual game, so this shouldn't require too much explanation. Just fiddle with it and you'll get the idea after a while. Once you're done, and all of your desired units and placed on the map and positioned correctly, press X on a blank space on the map and select 'Save', then close the playtesting window.
    Now, Unit Data is different from data created by the editors, as it's not immediately obvious where the data has been saved to. So go into your root FEXNA folder, then FEGame > FEGame > FEGame > bin > x86 > Debug > SavedUnitData. You should see a file by the same name as your chaper. Add this file to FEXNA in the same way you added your .map file and Intro event.

    Step 7 - Make sure your .map file is in Data > Map Data > Maps.
    Make sure your Unit Data file is in Data > Map Data > Unit Data.
    Make sure your Intro event is in Data > Map Data > Event Data.
    Make sure your Text file is in Data > Text.

    Step 8 - Start playtesting, select your chapter, and everything should work!