While it was clear that missile supply on a ship would be limited, I didn't find any information about "ammo", until I moused over a ship design and saw the ammo listed there and only there. Shouldn't the fact that ammo IS required and that the weapon comes with an amount of X ammo be part of the weapon description? I also find it strange that you cannot buy missile variants with more ammo (shouldn't there be an option, like "+100% ammo + 50% cost + 50% weight" or something like that?) ...
Missile ammo is displayed in the ship design screen in the weapons panel: You can set from 2 up to 20 missile ammo. Ammo is not a characteristic of a specific missile but of all missiles, so that's why it's not mentioned in the weapon description and is available as a weapon modification.
Well, if you didn't see that then it means it probably should be made standout better I took note of this and I'll see what I can do to improve that icon and text.
The icon is ok, but the 5 looks a bit camouflaged. Might help, if the number was beside the icon or beside and under it, like a foootnote or so.
you could put the five in an extra small colored circle in the low southern part of the icon (eg yellow or orange circle with black number, see included file) so that it cannot be overread anymore. (I guess the most important info for the player in this number-icon combo is the number so you should emphasize it - the icon is nice but large and thus good readable)