I hope they start at the Foundation itself, at least in terms of Hari Seldon establishing the original Foundation with the holographic recordings and the sense of excitement that happened when the first of these recordings started to play. Prelude to Foundation sort of ruins the whole
My hope is that they don't rush the Mule into existence soon in the series. It is a great story arc, but something that definitely needs to be about season 3-4.
Having the second foundation sort of hinted throughout the first season would be delicious though... if only in passing. The mental telepathy and manipulation of the second foundation would be a little tough to visualize, but I'm sure something could be made that way. Then again, keep it firmly in the background and only hinted at for diehard fans of the series to notice from time to time until the big reveal that would happen about season 6 (assuming it gets that far).
On the other hand, Prelude to Foundation could be used to flesh out production details for what Trantor actually looks like and some of the political situations on that planet. It doesn't need to include Hari Seldon's tour of the planet, but it is great source material that should be remembered for an eventual prequel if the production team ever wants to go that route.... or make a special "made for TV" feature length movie using the setting.
At least that is the way I'd do the production if I were the executive producer. I hope HBO doesn't screw this one up.