Hi Tchey!
As always, thank you for your feedback!
We weren't able to reproduce the crash you found, but we think we have located the issue all the same. We've released a small patch to address it. Let us know if it pops up again.
You make some good points about the Free Mode interface! It's still early in development, and we'll definitely be making some revisions in future updates.
With regard to Free Mode being broken, we haven't been able to find any issues. To place a character in Free Mode, left click on the character's portrait in the Free Mode window, then left click on one of the blue deployment tiles to place the character. Once placed, characters can be freely dragged around the deployment zone. To remove a character from your Free Mode party, simply right click that character in the deployment zone. Please also be sure to observe the party limit for the battle (shown in the bottom left of the Free Mode window). You will not be able to start the battle if you have too many characters in your party.
We will also aim to release a video guide for Free Mode soon. In the meantime, please feel free to hit us up with any questions you may have!