The consensus is that the medicine is out of your system by 5-7 days after stopping.
Acyclovir (and thus valacyclovir) was a drug specifically designed to treat herpes. The person who developed it won the Nobel Prize for this, Gertrude Ellion. It is not a general kind of antiviral. Your question is like asking me do influenza treatment medicines treat herpes. Not all antiviral medicines treat the same viruses.
Yes, 500 mg of Valtrex is the usual suppressive dose.
Terri