In general – great idea!
I would change the range thing though. Just let us set the range to desired number of spaces (enter a number or select from list)! It should not be hard to make it limited to min/max range of weapons on ships.
When it comes to targetting, id like to choose (add a tick) if my fleet shall continue attacking once attacked fleet till destruction, or not.
I don’t think that there is need for distinguishing current/starting max attack/durability for secondary targetting. Just make all current. You could keep killing same fleet by marking tick i wrote about earlier.