Thanks to Peter_22@xxxxxx and Jari!
Now I've just booted in encrypted root for first time!
You are right, it takes some time for kernel to find USB device.
INITIALDELAY=10 just worked good, 3 was to less. I think 4s could be good for me.
Sorry for delay, I had some problems with reiserfs. I agree, it would be better to answer sooner, but I wanted to complete this loop-aes thing.
Jari, I am really grateful about loop-aes!
Best wishes,
Jan