When exchanging Advantage points for anything else (like reducing Cost) the cheapest rates we ever get are when we are designing components, like right now. We should not anticipate spending any points to reduce cost or space used at the end, because that's the most inefficient way to go about it.
For the cockpit, I think we should spend 1 or 2 advantage on reducing cost if we can, and then bank the rest.
30 Cost and 30 Advantage are going to be difficult enough to reach that we need to be angling for that goal at every stage of the project.
Edit:
After doing some number crunching, I've changed my tune.
Small Strong 6 Double Deaths
Advantage: 33 + Bridge (5+)
Flaw: 10 + Bridge(0) -1d6
Cost: 23 - 1
Weapon: 12 + Bridge (bridge starts at 0)
Net 23 + Bridge(5+) + 1d6
Small Light 12 Double Deaths
Advantage: 51 + Bridge(5+)
Flaw: 16 + Bridge(0) -1d6
Cost: 29 - 1
Weapon: 24 + Bridge (bridge starts at 0)
Net 35 + Bridge(5+) + 1d6
I'm not really seeing where your math here is coming from.
Starting with looking at the Compartment Spaces, with the small cockpit we start with 16 but immediately must earmark 5 of those for the customer's Free Spaces requirement, leaving us with 11.
The smallest shield generator takes up 1 space, and the smallest military crew bunks takes up 2, so the maximum number of Compartment spaces we can use for Weapons is 8.
Your second option set has 12 Double Deaths though? Which makes no sense to me, unless you either forgot to set aside those 5 spaces or are deliberately not doing so, which I question the logic of.
If we use all 8 remaining compartment spaces on Double Deaths they collectively are worth 24 Advantages and 8 Flaws, for 8 Cost.
If we're using the smallest military crew bunks (2 Spaces, 1 Advantage, 0 Flaws, 2 Cost) and the smallest shield generator (1 Space, 4 Advantage, 2 Flaws, 2 Cost) that works out to:
Advantage: 7 + 4 + 1+ 24 =
36 (+ ~5 Cockpit)
Flaws: 2 + 2 + 8 =
12 (- 1d6 Q&A)
Cost: 8 + 2 + 2+ 8 =
20 (+ ~5 Cockpit)
This is... distressing. Our Costs are well within tolerances, but we can only barely get our Advantages up high enough to beat the Flaws by 30. If we assume that the bonus from our Dug cockpit engineer will manifest in other ways than more Advantages, and we don't spend any advantages on
anything, then a roll of 1 on the 1d6 reduced flaws roll will get us to Flaws + 30 Advantages by the
skin of our teeth.
Spending any advantages, or choosing options that earn us any fewer of them, means risking that 1d6 roll not being high enough.
Unless... do we know for sure that the requirement really means
net Advantages?