First, before you can even purchase the property that has missions. You need to do the Diaz kiling mission, not sure what it was called, check the walkthru on lisa's gta section. Then even after that, you hafta do a mission called "Shakedown" where u goto the north point mall and break all the glass within 5 minutes. Fairly difficult, but fairly easy if u have a goopd weapon.
If you still can't find any missions and you haven't done this stuff yet, Maybe check the bridge beside the huge mansion(Diaz's/Your mansion), normally if u are far enough there will be a red mission area outside the entrance to the house, and when you enter the mission, you and lance will invade the mansion, and kill Diaz. THEN you do the above missions.
Hope this helps, and check the walkthru.
