Can the marriage officiant who marries me also count as one of the witnesses?

No; an officiant who conducts the marriage as the wali's representative cannot be a witness to the same akad. In the Shafi'i madhhab, the wali and his representative are parties to the akad. So the two witnesses must be other people. The akad is valid if there are two Muslim male witnesses who are adult, sane and upright, and who hear and understand the ijab and qabul. The religious office or the officiant will usually make sure of this, but you can arrange two qualified witnesses in advance. Do not rely on guests who happen to be there. See conditions for marriage witnesses.