Is it okay to pray to the Holy Spirit?
One does not need to pray TO the Holy Spirit, dear one (peace to you!). One can simply speak with that One, just as that One speaks with/to such one...
Or, just to the Father?
The way my Lord explained to me is that (1) there is no "law" regarding it, truly; (2) so long as whatever one is doing is done is love, in which case, it's fine; however, since (3) JAH is the "hearer of prayer"... well, I will let you come to your own conclusion...
Jesus prayed to Father.
Well, since that One left us a pattern to follow, prayer to the Father is appropriate, yes?
Did he pray to Holy Spirit?
He is the Holy Spirit, dear one, with no need to prayer to himself. Thus, when he DID pray, he didn't say, "Holy Spirit... such and so..." He is recorded to have said, "Father... such and so..."
These Greek modalities confuse me!
Understandably. But you don't have to refer to them to try and understand; indeed, you are most assuredly wasting your time doing so. Much greater men (in the minds of some... if not their own minds)... have done so... and didn't get it... and are doing so, yet... and don't get it... yet. That's why you have all of the versions, and debates, and writings... to explain the writings... and the writers... and what this one wrote/meant... in contrast to what that one wrote/meant... if indeed that one actually wrote or meant anything at all... etc.
But you don't need to CONTINUE in your confusion... about God, Christ... or "Greek modalities." The Source is just as available to you as he is to me. He's there. All you need to do is ask. In faith. Indeed, you can even ask for faith. As one man is recorded to have said, "I have faith - help me out where I NEED faith!" You can ask that very same thing... and you will receive it... if you have faith [the size of a mustard seed]. Because that's really all it takes.
I bid you peace!
A slave of Christ,