I'd like to see huge bulk freighters and merchant liners, practically the size of capital ships.
None of the ships are built to scale with each other. Just pretend they're the same size.
How do I reduce the size of Gas Giants/Dwarfs and their gravity wells?
For the planet, you have to adjust the size of the mesh (both planet meshes, not included in DS but you can pull copies from the core game, as well as the 4 proto planet meshes which are included with DS), this is much easier if you have softimage, 3ds max, or something as the text version won't make any sense unless you actually can tell who is who by looking at lines of code in the matrix.
As for the size of the gravity well, that is much much simpler. Open up a text version of the entity, there are several in the gas giants case, near the bottom you will see lines for moveAreaRadius and hyperspaceExitRadius. You'll want to reduce those numbers.
Once you've done all of that business, the best thing to do is create a mod called little giants or whatever, in that mod folder, you'll need a GameInfo folder and a Mesh folder, and you'll have to put your edited files into their respective folders. Then when you're in the game and at the mod menu, make yours the very top of the list.