The second question part of the question is easier to answer than the first.

Firing by volleys was an innovation popularized by Maurice of Nassau and the Dutch army and first used at the battle of Nieuwpoort in 1600. Technically, his troops used the Arquebus and not the musket, but musket has become a more common term for all blackpowder smoothbore firearms.

The first question regarding "lines of musket infantry" rather depends on what you mean. Spanish Tercios were some of the earliest pike & shot formations to use tightly organized lines of firearm wielding troops, although infantry wielding firearms were not unknown before the Tercios appeared in the early 1500s. If you mean infantry formations comprised of entirely "musket" (i.e. not arquebuses, and not muskets supported by pikes) wielding troops, perhaps the Swedish Forces under Gustavus Adolphus in the 1630s were the first to deploy detachments of musket infantry that were supported by cavalry rather than pikemen. The pike did not entirely disappear from European infantry formations until around 1700.