Ill defer to the experience of others as I drink mainly espresso-based drinks (step up Mal ;)) but I believe steeping methods such as plunger dont tend to bring out as many of the oils / flavours of the coffee as the espresso process. As such a bean that has more varietal characteristics inherent and then preserved by a lighter roast will taste quite pleasant where it may be overpoweringly acidic through an espresso process - which I think is why low acid roasts (often darker roasts) are often recommended for espresso where in a plunger it may taste a bit flat.
I would encourage a bit of experimentation if you can... I cant see what youre using to roast, but if its a large batch corretto try pulling about 50g or so of beans out a few minutes after FC, and then do the same every minute after that until you want to stop the roast. Keeping them all separate, grind em up, steep and cup - thatll give you a fair idea of how they taste at different roast points and what you need to be aiming for.
As for bean type, SOs are always easiest to start with in the experimental stage, but try a bit of blending if you find youve got the right roast level in a particular bean but its lacking a bit of something.