Civilians do not care how viable in combat a ship is, only that it has a big scary gun. You can make an engineless husk that is carrying a laser or railgun and build a couple of dozen of them to make sure that the PPV rating for Sol is high enough until you build an actual space navy.

While it's not, strictly speaking, the best idea for your battle fleet, I tend to design the largest engine I can for my ships, such that one or possibly two engines provide all the power needed.

Pros: Gains in fuel efficiency (potentially large ones, especially in tiny things like fighters).  If you don't need the extra fuel efficiency, you can overcharge your engines such that the total fuel consumption remains static, but your ships move faster under the same engine tonnage.

Cons: The engine(s) are, by far, the largest target on the ship, so get hit statistically more often.  If a hit destroys the engine, you're either stuck in space or down to half speed.