True. You need at least 2 physical disks.
Pointless. The point of a RAID 1 array is to have two identical copies of the same data over two disks so if one fails, the data is fine unless you're really unlucky and both die at the same time.
Plain stupid (no offense :D). When the drive fails, it will take out all your data. No point in doing a RAID-1 then. Also, you essentially halved your storage capacity since, as mentioned, you need to have two exact copies of the same data. It will also be slow since it needs to write data twice. I'm aware you're aware of the capacity halving issue but there's also the speed factor.
Cumbersome. You need to hack the kernel to make it recognize your drive partitions as two drives.
Utterly pointless. I'll say it again. The point of a RAID-1 array is to have two copies in two drives (2 drives) so if one fails, the other has a copy. If you use only one disk, the essence of RAID-1 itself is undermined. You're better off using all of the disk's capacity.
The only benefit I can think of is that if there's a disk head crash, the other partition not covered by the damage will hold a perfect copy of the data. The problem is that you need to send it to a data recovery company since, as mentioned, the disk head literally crashed and scraped the platters.
In short, you won't avoid losses.
In shorter short, it's possible, it's superbly practical, and you should totally do it (sarcastic tone).