FCP 7 Export via Compressor for DVD Studio Pro Mastering

I've seen some posts that are dangerously close to answering my questions, but here goes. I've got 2 SD sequences in FCP 6.0.6 which I need to export using Compressor to then burn to 2 DVD-R's with DVDSP. The sequences are 2 hr 30min and 2hr 50min. The material consists of downsampled HD footage (school Christmas pageant) as well as a number of slideshows of still images w/blends and there are text overlays throughout. The footage is a 3 camera-edit, so there are cross-faded throughout the 2+ hours of footage:

1) I've gleaned from David Roth Weiss' posts that I should indeed be editing the QT Video Settings in the Sequence Settings in FCP to pick an optimal compression algorithm for exporting, right? What is specified here will be used for the export via Compressor?

2) Previous posts referred to using Prores 422 for this setting. Why would I not be using H.264 here? Also, were you in fact recommending the HQ version of Prores 422?

3) Can you advise me on the settings to use in Compressor? I've seen a tutorial that walked through the DVD presets which indicated that the 150min setting was adequate for 2 hrs and above. This seemed like a rather general piece of advice and I'd rather get advice that is more dialed into insuring that my specific media will fit on the discs with good quality. How do I best calculate this? Is there a way to preflight a few seconds of the footage to see what it will end up looking like?

4) What is the maximum footage (realistically) that I can get away with putting on a DVD? I'm sure a "depends" is in the answer, but how about in my case, with the material that I described above?

5) FWIW, I have a rather old Mac, so my rendering speed in any application is quite challenged.

Thanks a lot for your help! In the 11th hour here (of course)!

- Drea