You can use any bread you like but I wouldn't recommend a very grainy bread. In my experience the grains turn out a little rubber-like.
After the frying I added a little more butter of a richer buttery flavor
In general any butter is possible though I think the spicier it is the better it gets. I can't wait to try this once I've made Sriracha Lime butter the next time.
I haven't tried this but I imagine a little crumbled feta on top would be divine!
*** Update*** I tried this with feta and black olives and it's indeed pretty darn divine!