Please see the update to version 0.4.6. You can pass parameters to the native gallery, including columns.
[content gallery="native" columns="6"]
Changing the spacing for the native gallery doesn’t seem to be straight-forward. It’s possible to build your own gallery using [loop] and [content], and style it how you want with HTML/CSS. Here’s the basic form:
[loop field="gallery"]
[content field="thumbnail"]
[/loop]
I’ve been thinking of adding a basic responsive gallery, but I’m afraid it will have to include a CSS file, and I’d like to keep this plugin as light-weight as possible. I’m starting on another plugin for simple responsive layouts, so I can include a way to display a gallery field. If that’s something you’d like to see, I’ll work on getting it completed soon. ??