You need something to boot homebrew first. I use the broadband adapter with PSOLoad, but there are other ways to do it. Stuff like SD Media Launcher works too.
Also, SD Gecko is pretty simple. Heres mine I made a couple weeks ago! Just used a Micro SD card adapter, so this is pretty much a micro sd adapter. You can seek out a regular SD card slot thing, with the push click but I have so many of these adapters around I sacrificed one.
On the GBI front. Its just not possible to use the low latency versions with XRGB mini. It wont recognize the weird refresh rate. And no 240p out of Component either. Fuckin bummer!! You need a PVM / CRT for the low latency version it seems.