Some additional commentary:

2. Deinterlacing:

The input PAL DV source file is Interlaced, Bottom Field First
... 
Why does deinterlacing with dvd default rendering (mpeg2enc) still come out as Interlaced, but Top Field first?ffprobe -hide_banner dvd.m2v
I have been looking for any information on this and lots of testing.  As far as I can tell, whenever you Render or DVD Render, it seems like the Interlace always comes out Top Field First.  I have not found a way to get Bottom Field First but have not tried all render formats (which I will continue to look at).  It may be that it only does Top Field First or Progressive.

3. Dvd Interlaced Chroma

With reference to the CinGG manual
https://cinelerra-gg.org/download/CinelerraGG_Manual/Dvd_Interlaced_Chroma.html
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I can't find this option and is it relevant for DVD rendering?

This needs correction in the manual. (Hopefully you found it in the screencast Andrew mentioned). It is Settings->Preference, Interface tab, 4th box down in the Operation section.

TO BE CONTINUED as time permits.