Hi there. The toolkit is not built with massive, continuous worlds in mind so if this is your end goal you will need to to quite a bit of modification. The best approach depends a lot on the requirements of your game. This is also not something I have tested myself, so my suggestions of what will work best is based on a fair amount of guesswork.
If your game world is real time and free-roaming until combat begins (like in Fallout 1 or 2, for instance) then you can have movement controlled through some other means and when combat starts, place down a grid manager encompassing the combatants, running grid setup, adding the units to the grid and starting combat. For large grids or if the grid manager uses a lot of procedural grid building options this might cause you to drop a few frames, though, so manual conversion of startup functions to C++ would be recommended.
Other options might be possible depending on your requirements. How is your world built? Do you have multiple overlapping levels? What is the maximum movement and range of units in your game? Is it important that units can keep moving to any tile anywhere on the map even after turn based combat has started? Do you need to be able to display the entire map at any time for the player to look through?
I would probably not recommend trying this if you’re just starting out as a programmer or with UE4 generally, but I might be wrong, of course. It might be that you can achieve your desired results through only moderate modification of the toolkit, or you might have to build a lot of it from scratch. A bit hard to tell beforehand, unfortunately. This is the sort of thing I would want to test out personally if I had more time, but time is in very short supply for me at the moment. Let me know if you make any progress or have any additional questions.
Thanks, that is very kind of you 
You got the name sloghtly wrong with Advanced Turn Based **Grid **Toolkit instead of Advanced Turn Based Tile Toolkit, but that is my bad for choosing such a horrible name in the first place. There is a story to why the name is so bad and I regret the choice daily 
Hello there! Although the examples used in the toolkit lean toward an XCOM-style I have always tried to develop it with all sorts of grid and turn based games mind, so it should hopefully suit your needs. The ability system is created both as a system for abilities that can be activated, but also as a practical way to encapsulate and make modular AI and other game functionality. It should be a good fit for most abilities that are activated and have explicit effects. For a skill like say, persuasion, that simply confers a bonus to some game aspect that all characters can do you can get away with just using simple variables or data tables.
Turn Based Toolkit in Unity is made from a different developer so I can’t be sure when it comes to what features it has.