Ugh, I checked a couple of different ships I'd made and they all had -5000 for the astrogator salary... then I realised the "-" was a speck of dust on my screen. I'm sorry for wasting your time with that.
For the small weapons, HG p40 says fixed mounts cost 5000Cr per weapon (plus weapon cost) regards of their size, or 50000Cr for a pop up turret. The sheet appears to be charging 1000Cr per space of weapon or 1000Cr for a 1 dton turret. Also can't create a turret smaller than 1 dton, should be able to have a 0.25 dton turret for weapons that mass less than 250kg. Thanks for looking at this, I know small weapons are not a focus of ship design, but I'm currently recreating a couple of TNE designs that have small weapon mounts.