You can see a complete list of group header attributes in the Blizzard UI code:
https://github.com/tekkub/wow-ui-sou...eaders.lua#L24
However, not all of them may be applicable to oUF party frames, and not all of them may interact with each other as expected, or be supported by the particular oUF layout you're working with. Proceed with caution.
Re: options, most oUF layouts don't have any. They're so easy to write that most people just write what works for them, and maybe throw in a few basic options like font or bar texture selections, and that's it. It's generally expected that if you want something different, you either write your own or at least make your own changes, or you just use a more configurable addon like PitBull, Stuf, ShadowedUF, etc.
That said, writing oUF layouts is very easy; if you want to learn how to start from the beginning, I'd recommend looking at one of Haste's example layouts (oUF Lily and oUF Classic) as his code is straightforward and easy to follow, unlike the code in some other layouts that are advertised as examples (eg. oUF Simple isn't badly written, but it's really convoluted and way more complicated than I'd ever give to anyone as an example of how to write an oUF layout or a WoW addon in general).
If you just want to learn how to make changes to what you've already got, adding support for additional units requires editing every part of the layout that includes any unit-related conditional checks, so it's not really something I'd recommend as your first project. Try some simpler things first, like moving a font string, resizing a texture, etc. until you're more comfortable with the Lua syntax and basic WoW API functions.