Tire guards?  Do you mean tire covers?  If that's what your asking about, then take a tape measure and measure the tires diameter and pick the size that is equal to or larger than that measurement.
How much sewer hose?  Depends.  I normally have a 10 foot and a 20 foot piece on board with the appropriate connectors to put them together.  I have used all of it more than once.  Right now, I am adding another 15 foot piece because the place we will be at next month the storage tank is a ways and down hill from our site.  If you have two dump locations then you will also want a "Y" connector and probably two 5 foot hoses in addition to the longer hoses to get to the sewer dump.