Thanks again for your feedback!
* Tooltips for the upgrade screen should be fixed.
* Indication when placing the core is fixed, you can cancel placing a core by right clicking.
* I'm not sure what to do with the health bar yet, how it works now is, you have 1000 life over several rounds, whenever the enemy destroys a block from player ships this will go down, when you reach zero you lose. This will probably be replaced by adding a static base structure the players can build upon every round, and has to be destroyed for the other player to win. the damage to a static base structure will be permanent unlike ships which regenerate each round. You will be able to place almost any block on it like you do with ships, one of the exceptions will be no engines. I'm still not decided on this, it's just an idea.
* As for the core mechanics, lots can be done with it, I do prefer being able to split ships in two or more pieces and they work individually, while the engines provide physics based propulsion. However just one block with a weapon seems kinda dumb to be honest :) I'll think about this.