Use the "remake a DVD" option. Then navigate to the video_ts folder (presumably on hard disk) containing files. Nero Recode will then analyse the folder and tell you how many titles there are (say 4). You can then select these and add each to the workspace.
Then you might navigate to separate video_ts folder with another 4 titles, and also add these. Nero Recode will automatically adjust sizes. Then you "burn" these to another folder (recommend only burn to hard disk so you can check results) and all 8 will be in one folder. Note: with Nero Recode, you can eliminate unecessary soundtracks e.g. foreign languages or directors commentary etc which minimises degree of shrinking required)
It is difficult to be precise about how much you can shrink a file as it depends on how much movement (fast films do not shrink as well as slow films), what the original bit rate was, audio type etc. Personally, I do not shrink to less than 70% of original size. Below this, I generally prefer to use two disks.
Nero Recode is quite fast (about 30 mins for processing a full DVD and 15-30 mins to burn depending on speed).
It is better if you have two hard drives (i.e. read files from one and "burn" to another) as this helps speed things up..
The use Nero burning ROM and drag files to video_ts folder on a new DVD and burn.
The major downside to Nerio Recode is that it doesn't create menus. You will have to use remote on DVD player to change between titles - not a big deal.