also make it so that if missiles in a salvo hit they also have a chance to destroy missiles in the same salvo before they impact the target. This is quite realistic...
I don't think it's realistic, remember that we have warships a few 100m in size that thanks to TN materials can be protected from direct nuclear blast impacts, so we have to assume that the missiles have at least as advanced shell to protect them.
If a salvo of ASM travel at 20,000km/s they can cover 100,000km in each 5 sec increment, so let's assume that the salvo will spread out the missiles in a volume roughly representing a sphere with 50,000km diameter ( all missiles will impact within 2.5 seconds). That sphere covers 60 times as much volume as the entire planet Earth does.
I doubt the missile hull needs to be very thick to survive a minimum size yield warhead so far away.
Collateral damage to ships in formation in same fleet would be a bigger concern IMO before this is since they are bigger targets and they may have other reasons for staying in closer formation then missiles do ( such as transferring fuel/ammo/crew/data )