I think all up you are merely creating a rod to beat your own back with!
If you are talking about an actual video DVD like the ones you buy with commercial movies on it or rent from DVD rental stores, then the format has to be mpeg-2 by international standard. Then there is the question of bitrate, and thus quality. With mpeg-2, a bitrate of 4000 kbps will allow about 2 hours of video to be burned to a single layer DVD and 4 hours on a dual layer DVD. The quality will be around the same as a VHS tape. You can squeeze in more video by lowering the bitrate but the quality then drops off dramatically. With a single layer disc, it would simply not be worth your trouble to try to squeeze 10 hours onto it as the bitrate would be down around 1000 or 1500 kbps and the quality essentially unwatchable. You could do it on a dual layer disc by dropping the bitrate to around 3000 kbps or lower, but the quality still wouldn't be good.
And if you're thinking about those DVDs you've seen in shops that have 5 or 6 Hollywood hits from the past squeezed onto them, they are produced by pressing after the video has been processed through programs and equipment worth tens of thousands of dollars in order to squeeze every last possibility of space and quality out of them.
The only other option would be to create a DivX disc using either the DivX or XVid codecs. Your avi originals are probably already in that format, and just about all DVD and Blu-Ray players can also play DivX movies when they are detected on a disc in that format. But even there, while it could notionally be a bit better than the mpeg-2 route, you would be having to drop the DivX quality standard down to where the end result will barely be watchable. And you will be aware that DivX/XVid videos are very prone to pixellation and other distortion artifacts when their bitrate is dropped too much.
So overall I think the option of 2 or more discs is looking the most viable...