I believe Paul is correct; God refers to Himself in the trinitatrian pluralistic sense. It is also interesting to note that revelation speaks of
"seven spirits of God" [Rev 4:5, 1:4, 5:6] (more specifically translated to "sevenfold"; Hepta=sevenfold).
"Before the throne, seven lamps were blazing. These are the seven spirits of God." [Rev 4:5]
"Grace and Peace to you from Him who is, and who was, and who is to come, and from the seven spirits before His throne, and from Jesus Christ, who is the faithful witness..." [Rev 1:4]
Here we see that Grace and Peace are ours from three persons: 1) Him who is... 2) seven spirits 3) Jesus Christ. This is not to say that the Holy Spirit is seven person's, but rather, that the Holy Spirit is seventhfold; complete in perfection of glory, in seven characteristics.
Now take these verses in Revelation in context to what the Church teaches regarding the
seven gifts of the Holy Spirit;
1831 The seven gifts of the Holy Spirit are wisdom, understanding, counsel, fortitude, knowledge, piety, and fear of the Lord. They belong in their fullness to Christ, Son of David. 109 They complete and perfect the virtues of those who receive them. They make the faithful docile in readily obeying divine inspirations.
What's more, is that the Holy Spirit is active through the seven sacraments that Christ gave us; the seven characteristics of the Holy Spirit extend to us in grace through an action that we are called to partake in, as our response to God.
Anyway, just some random thoughts.
May the Lord give you His peace!
-Davide