Hi Kristjan. The most important advice I can give at this point is to immediately forget you're working with a touchscreen. It's easy to lose yourself in cool gadgets like that, and forget to build up a solid base.
The touchscreen will be part of the graphical representation and controller of your application. First focus on the actual game mechanics. Create a package that will contain classes such as BattleGround, Creature, Player, Interactive (for objects on the battlefield creatures can interact with).
At first you can
test your model using the console. Just display the game in some Ascii representation. This is of course, assuming that your game is turn based (which is the case for most grid based games). You can just print the state of the field to the console after a player's action. (
You should probably start testing with small battlefields).
Finally, when you're done with your model, you can start working on the visual part. Again, forget about the touch screen. Just make a standard graphical application in Swing, and perform manipulations using mouse/keyboard.
When this is done, you can add event listeners that deal with touch screens. Often, this won't even be necessary, because I would assume most touch screen manipulations are already handled as if they are mouse operations.