There is definitely some misunderstanding here
First: USB stick is for booting, questions about this are already answered. (stick can be very small, will never be written to, etc.).
But your second questions is about hibernation. To make sure your system can hibernate, the disks need to be idle. If you write a lot of logfiles regularly to the disks, they never become idle, so the system will never hibernate.
To solve this, you can move those logfiles to a USB stick. I'm not sure if it's a good idea to use the same USB stick you use for booting.
Easiest is to use a second USB stick for this. This can also be small, but 64MB might be too small. I think 1 GB should be enough for logfiles of SABnzbd, Sickbeard and CouchPotato.
Just try and see if that solves the hibernation problem.