Interesting build. From my own experience with the Fer De Lance a few thoughts have cropped up.
1) Scooping cargo (or anything) isn't easy on the FDL due to the layout - the collector limpets you have allowed for may be a good idea - but they take up cargo space of which you don't have much ...
2) Weapons loading is a very personal thing I know, but for me the issue here is that the rail gun ammunition will disappear very fast. I would go for 4 gimballed class 2 pulse lasers and a huge gimballed cannon for the big ships. The ship size vs weapon class issue relates to damaging hulls, not the shields, so there is effectively no penalty for using (more) medium size lasers for shield stripping, even on larger ships. The class 4 cannon would carry plenty of ammunition for an extended stay out in the field. This would reduce power usage and heat generation too so you wouldn't necessarily need the heat sink launcher.
3) You will need the class 5 module slot for cargo so a class 4A shield generator is not a bad plan. You could consider signing up with Aisling Duval for a few weeks and obtaining a Prismatic shield generator for this slot - yes it's heavy but it would give you the best shield possible for this slot. (Effectively a 5A).
4) I would go for a class 4 frame shift interdictor (for range) (4D is my preferred one for the FDL due to its low weight), and have a smaller collector limpet controller.
5) The discovery scanner is always nice to have but with limited slots would it not be better to have this slot free for the collector limpet controller?
6) With limited range and fuel tank, I would want some kind of fuel scoop - a class 2A would at least give an option to stay out in deep space for longer.
7) The biggest issues I have with my FDL are its range and its turning ability when fully outfitted and fueled. The Military grade composite armour in this loadout is going to add an awful lot of weight to this ship. Ideally the laden weight should be under half the optimal mass for the thrusters. That's 420 tons. This build is getting on for 50 tons above that, 38 of which is the armour.
Its an interesting question, and those are just a few thoughts.