1. What do you mean by safe? Safe might mean almost anything. From not
getting raped in your own home to not getting bad sectors on your hard drive.
2. What do you mean by trustworthy? Trust, as safe above, can mean almost
anything.
You can also take a look at SD cards which come with a lock switch by
default. Booting them should not be more complicated than booting a regular
USB stick.
Finally, once things are more clear for you, you can go ahead and contact
Moritz Bartl[1] who has done some actual research in this direction.
3. Don't get it.
4. Never heard of encryptedFAT. Is it supported by the Linux kernel?
[1] http://comments.gmane.org/gmane.network.tor.user/29632
