Most of these questions should probably be directed to the local tv station that will be showing your stuff. But…
1. It’s not the size you need to worry about, it’s the bit rate. I do a lot of work for Yelp, and they require 15 mb/sec. Now, that’s a little low for my taste, but it will still give you a solid image.
2. Based on what I understand from your post, it seems like your workflow is fine. 25 mb/sec should really be just fine. Of course when you go to put on DVD, it will get compressed, more than likely. But I always let the computer do that work for me when I go to author the disc.
3. A DVD can hold 4.6 GB. So 3 GB will fit. But again, check with the tv station to see what they prefer. Also, do your math. 8 bits equals 1 byte. So 25 mb/sec comes out to about 3 (and some change) MB/sec. So at 25 mb/sec, you’re looking at around 16 minutes of video only. So, you’ll need to keep that in mind. A DVD will usually only play at around 8 mb/sec.
4. See calculations above.
5. Check with the tv station.