Number of Agenda Cards Scored
Agendas typically follow the same rules for deck composition as any other card in Netrunner.  This means there is a maximum of three copies of the same card allowed in a deck. Either player can score multiple copies of an agenda, especially if the reward for scoring it aids their playstyle (e.g., using Priority Requisition to rez big ice in a glacial build, or Astroscript Pilot Program in a fast advance deck). 

There are a couple exceptions to this rule, but they will say specifically on the card that only one can be included in a deck (the most recent card like this is Jinteki's Philotic Engagement). 

If you are playing core only, you should take all of the faction specific agenda AND all of the neutral agendas for your deck. This will mean three copies of Priority Requisition, and Private Security Force, plus the in faction ones. In a typical built deck (49 cards), you will need 20 agenda points to be in the deck, made up however you want from the available neutral and in faction agendas.