You might also consider one of several Reaction Engines for when running "hot" - a few of the superscience ones outperform the Standard & Hot Reactionless Drive on thrust, and thus make a great secondary drive for combat or short bursts (such as landing and takeoff).
Spaceships 7 is definitely the best expansion of ship systems, although probably half of them are "weird" tech that you're not likely to use unless you're doing a "weird" tech game - orgone and mana engines, Skystone for airships, that kind of stuff. The other half is still outlier tech, but more generally useful to Sci-Fi; it also repeats the rule for Smaller SM Systems from Spaceships 4, which is one of the most useful rules expansions given the diversity it adds to creating spaceships.
Two other resources to consider are
Pyramid #3/34 and
Pyramid #3/40. #3/34 includes a rules expansion for realistic ground vehicles - Wheels & Tracks, Screw Propellers, Gasoline Turbines, etc. Pyramid #3/40 includes an expansion for Mecha & Robots which greatly enhances the rules from Spaceships 4. If you plan on making Mecha a central part of your game then it's well worth picking up.
Pyramid #3/64 also includes a few other expansions for Age of Sail/Steam Tech.