These are great suggestions! I considered double click to buy and sell, but we were concerned it would be too easy to trigger accidentally. We can give it a try though, I agree that the drag and drop is a bit tedious.
Ship efficiency is a function of how many modules you have, and is a multiplier to your cooldown progress in each module (so a ship with 50% efficiency only activates a generator every 2 seconds as opposed to the 1 second cooldown at 100%). I can add more information about this to the game, and we'll be adding ways for you to increase your efficiency with modules and potentially your ship's crew if that's added.
Trading is definitely the most rewarding path right now, I think you're right that combat rewards should be increased. I like the idea of salvage rewards as well, although it could be hard to fit into the narrative. Like if you take a ship's gun then in the next system you see them again and they still have the gun. It's worth considering though, I like the idea of being able to take a less destructive approach to try to get a higher reward.