You can actually do any of those ideas and they will work. To save yourself the time, you only really need to write out an example intonation once, and then it is assumed (at least in the LU) that the example applies for all of the text that follows. You still have to point the text, though, so make sure to be careful in doing so to ensure that they will work for your chosen termintation formula.

I'm doing something similar: I am using the antiphons from SEP, then chanting the verses using Gregorian psalm tones from the LU. Of course, I have to repoint the text.

If you are seeking to publish, I'd urge you to reconsider. What you are asking is allowable, though perhaps inadvisable, especially in a bound collection. It gives the impression that all one needs to do is sing the texts (in translation) to Gregorian patterns.

Form matters, as you understand since you asked the question. On a bigger level of form, the office should sound different than the sacred liturgy, our highest prayer. The two have always been musically differentiated for good reason.

I'm aware of the use at St. Peter's and beyond. The psalm tones are used to extend the Introit (or Communion) because the litirgical action takes more time. One hears the antiphon and the psalm tone, alternating. Of course.

But to have only psalm tones used for a long time, especially in the case of an ordination, would get tedious pretty quickly. Sure, it's better than a lot of things that could be sung. But it's still not a great idea, and it gives fuel to those who claim that Gregorian chant is boring.

Gcasa,
Sincerely, I do not mean to be discouraging of your efforts in general.
I have been in the situation where more solemnity is called for and yet Gregorian chant is still not desired. I've also been in the situation where organizers do not want Latin but would like simplified chants in the vernacular.

As to time and compositnal ability, I do have some suggestions for you. In order to avoid a texture (psalm tone only) that is too plain for te solemnity you desire, you might:
1) ask someone on this forum- one who speaks of is at least familiar with your language- to arrange a simplified introit for you. Many here would do this free of charge. I would also volunteer, and free of charge, especially because this is for an ordination. Then, alternate that arrangement with the psalm tones.
2) alternate the psalm tones with organ improvisation if your organist is comfortable with that.
3) choose a dignified vernacular hymn, and then use the psalm tone proper when the ministers reach the sanctuary.

I'm not sure what country you're in but it sounds an awful lot like our situation in Quebec. Our schola does do Gregorian chant from the GR (once a month at different parishes), except we do the responsorial psalm instead of the Gradual, and we do it in French which is our vernacular. We face the same hostility as you do with regards to Latin, chant, pre-Vatican II, blablabla. Fortunately we have found some parishes willing to risk hearing us. We do the Ordinary Form Mass exclusively (more because that's all there is in the small city that we're located).

That said, have you considered the option of the following the Graduale Simplex instead of the GR? The antiphons are much simpler (along the lines of the Divine Office), and the psalm tones are the simple ones for the psalm verses. So you have a somewhat more ornate melody for the antiphon (but not as much as the antiphons in the GR) and simpler psalmody. There's still a contrast, and the melody of the antiphon may be much easier to adapt to the vernacular.

If you do follow the Simplex, the formula follows your first example.