1.) Both are on Namek
2.) Win by death
3.) I was under the impression pre and post crisis Darkseid are the same person, due to a John Ostrander issue of Firestorm mentioning that Darkseid remembers pre-crisis events. If that isn't the case, then both Pre-Crisis and Post-Crisis feats can be used anywa for this fight.
4.) If Darkseid is on the losing end, post flashpoint feats can be incorporated as well on top of what pre-flashpoint DS already has.
5.) Final form Frieza; if he loses, then King Cold can jump in and help.