Unfortunately there isn't a way to have an editable text layer as a layer mask directly in GIMP. You need to use Alpha to Selection to make the selection in order to make the mask. However what you can do, is retain the editable text layer if you ever need to make changes, so that you can easily create a new mask. You can simply hide the text layer by clicking the eye icon next to the text layer in the layers panel. Then save the document as an XCF, for future edits.
You could certainly use layer blending modes, but it wouldn't be an actual layer mask as such. Also some experimentation would be required I think. Offhand, and without seeing how the rest of the layers are constructed, I couldn't just say use such and such a blending mode.
However here's an example where it could work. I have typed the layer modes in the layer descriptions so you can see them.
