Hi! Wow, thank you for such detailed feedback! When the carriages detached, that was actually a bug :) Normally, all carriages should be destroyed, not just detached.
As for displaying health — you can't have a health bar and label for every carriage. But take note, the dimmer the carriage, the less HP it has. Just like with the enemies, brightness is the indicator.
Yes, if you're not moving, you're not shooting. I now realize that this function isn't really necessary. However, it's the main reason why I could participate in this jam, since the limitation was 'One button - two functions'