Just seeing this with the new responses. I have brewed a coffee stout once or twice a year for almost 20 years now. My personal favorite method at this point is adding the grounds at flameout (basically like a whirlpool addition) using a fine mesh nylon hop bag. I find it gives the best balance of coffee flavor and flavor stability and longevity. I really like the granularity of using a cold-brewed concentrate (with my Toddy setup), but I've found that the coffee character fades a lot faster using this method. If I were brewing a batch for a festival where it was going to be consumed quickly, I'd probably go with that, but for around the house, flameout is the way to go for me.
As far as what type of coffee, you need to ask yourself that. What type of coffee do you like to drink?
When adding at flameout, how long do you steep? Just through chilling?