Author here. First, space combat is obviously not the focus of the campaign, so the rules are more for GMs who want to branch out. That said, I think you've hit the right spot.
When you roll for damage effects and roll an area that has 0, the result above it applies, which means that area instead loses one point. If that area is reduced to zero, the effect triggers. If hull is affected but has 0, nothing happens (you are in effect already floating in space in a shot through sardine can).
Space combat isn't meant to have a specific end point. It is an event in an adventure that can lead to other things. So when the end of space combat is depends on what you mean with "end". Maybe you want to shoot out the engine or board them or just leave a mark. The thing is that even if you fire holes into a space ship, it will still keep moving through space
. So space combat might be prolonged if the only true end state is that the other ship is blown out of space.
There is indeed no rule that says you can't hang out the airlock and take potshots at the enemy ship with your pistol. And the rule of cool suggests that you do just that
. Note that you need to make more damage with your shot than the space ship's resilience for it to have any effect. Typically the space ships in Ad Astra are not double-hulled, well maintained, combat worthy starships, but sardine cans with fusion reactors. Shooting at them with guns can be very effective!
It's a bit of an omission to not give Mundilfari a resilience score! It should have Resilience 2.