How likely is a fever associated with fifth disease?

Yes. Parvovirus b19, the virus that causes fifth disease, can also cause fever and other flu-like symptoms in about 50% of cases. Normally though, by the time the facial rash that characterizes fifth disease arises, the fever and other flu-like symptoms have subsided.
1 in 5 will have one. Symptoms of fifth disease (aka erythema infectiosum) come in two phases. About 1 week after exposure and lasting 2-3 days, the first phase symptoms of headache, fever, sore throat and itch are common in approximately 20% of cases. There is a symptom free period for 7-10 days before the second phase occurs which involves a rash on the cheeks or body. It is no longer infectious when the rash appears.