Re: 720x486 question

I'm not familiar with that format either.
I'm pretty sure DVD use 4:2:0 color sampling, although MPEG-2 does allow for 4:2:2.

720x480 is DV. 720x486 is D1.
DV refers to both a frame size and a codec.

It's probably a good idea to familiarize yourself with the acceptable formats of your DVD authoring software, and set your project spec's accordingly.

Premiere Pro with the HD addon does allow for a 4:2:2 color space, but I think it is only for resolutions of 1280 X 720 and above.

As far as Premiere automatically cropping, that's in your project settings. It is a setting that can be changed while you are in your project. It will either crop larger frame sizes, or you can set it to scale clips to fit the frame when they are dropped into the timeline.
If your video is interlaced it should not be scaled, you will lose quality.
If you are going to DVD and you are working with a frame size that is greater than DVD, you'll have to either crop or deinterlace and scale the frame to fit.

The rendering quality is your choice. You can render as uncompressed AVI and you won't lose a thing. Both DV and DVD compression will generate compression, naturally.
Ideally you might want to have something like Main Concept MPEG Pro so you can encode your edit straight to DVD-Video MPEG-2. The benefit of MPEG Pro is that you have a great deal of control over the encoding process.

If you are going to DVD, there should be no reason for concern in using Premiere.

If you do need to deinterlace for resizing, I'm sure there are plugins that will do a fine job, however I've never used them.
I have always deinterlaced in After Effects with Fields Kit Deinterlacer than export as Uncompressed for editing.

Just some thoughts, hope this helps

Vince