[dataweaver]

Don't worry about time travel shenanigans; that assumes that FTL Drives are compatible with Einstein, whereas generic Space Opera assumes that FTL supercedes Einstein, or ignores Einstein entirely.

I'd make reactionless drives dependent on Hyperdynamic Grids (from Vehicles Expansion 1): they're not truly reactionless, it's just that what they react with is in hyperspace rather than normal space. This imposes a top speed on them, limiting their usefulness as kinetic kill weapons, and plays up the “wet navy and aircraft” tropes for which so much Space Opera is infamous.

Go with TL10+force fields, possibly allowing for something like the swashbuckling option mentioned in several editions of Space (where high-energy attacks are stopped far more effectively than low-energy attacks). Apply this notion to planetary shields, and you largely remove the incentive to try for Station Drops and possibly even orbital bombardment while still allowing for troop transports and carriers to project power.

(In the setting for which I originally developed these ideas, I had a sort of Unified Theory of Superscience, where everything marked TL^ was in some way dependent on hyperspace. As such, there were no dedicated Hyperdynamic Grids; instead, force fields doubled as Hyperdynamic Grids where it mattered.)