Managing your finances is a huge portion of difficulty, so anything along those lines would be great.
- Mission reward scaling
- Generic salvage scaling (supplies/fuel/etc)
- Fleet Upkeep (crew cost/supplies/etc.) scaling
I dunno how well an "expedition timer" will work in terms of difficulty. A lot of expeditions can be trivial if they're all tiny, while a small number of expeditions can be brutal if they're monolithic attacks. Generally players get more annoyed if attacks happen too frequently, since that takes time away from other tasks they may enjoy. It'd probably make more sense to adjust the enemy fleet difficulty rather than the frequency of events.
Fuel is something that is generally very well displayed to the player and doesn't really require a difficulty setting. If anything, adjusting fuel expenses would only screw players up by giving a rock solid impression that ends up completely obsolete when the difficulty changes. It'd probably be better to adjust fuel recovery from generic salvage, so that easy mode is easier to sustain in deep space. Maybe there could be more forgiveness on distress calls as well, since that's the player's safety net if they run out.
Should difficulty interact with trade settings in any way? A sector in shambles may suffer with resources, but beat down planets offer superb trade opportunities. Similarly a very rock solid stable sector will struggle to offer big money trades. It doesn't seem like a direct 1:1 with difficulty, but is more about setting the theme of your sector.
Don't forget that a very small change in many areas can add up and multiply together into a vast swing of overall difficulty. While a lot of tiny dials are enticing for an experienced modding community, new players should not be expected to understand any details on the difficulty system. If they want easy, selecting easy should be easy.