Does 1 cockroach mean there are more?
Generally, yes. It would be very rare and very unlikely that you could ever have just one roach. Roaches are social insects and prefer to be around each other. In addition, roaches breed rapidly, so most likely the roach you see has already reproduced another generation. It is best to assume that when you see one, you have many and start taking the necessary steps to eradicate the problem.