Dear Henrik:

The Mass is the highest form of prayer in the Church. The Liturgy of the Hours is the second most important prayer in the Church, followed by the Personal Devotional prayers, such as the Rosary.

The Mass and the Liturgy of the Hours, being official prayers of the Church are regulated and must be said according to the rules set by the Church. The Personal devotions, such as the Rosary, are not regulated by the Church.

In heaven, there will be no Masses, as we will be in the presence of the Risen Christ.

St. Thomas writes (S.T. III, Q. 22, a5):

The Saints who will be in heaven will not need any further expiation by the priesthood of Christ, but having expiated, they will need consummation through Christ Himself, on Whom their glory depends....

As Vatican II stated in the Constitution on the Sacred Liturgy (#8):

"In the earthly liturgy, by way of foretaste, we share in that heavenly liturgy which is celebrated in the holy city of Jerusalem toward which we journey as pilgrims, and in which Christ is sitting at the right hand of God, a minister of the sanctuary and of the true tabernacle."

The prayers of those in heaven are the most powerful of all because they are saints in the presence of God and are perfected and are righteous. 

The Mass is the most important prayer on earth as it is a foretaste of the heavenly liturgy, which will not be a Mass sacrifice but a consummation through Christ Himself personally.

Hope this helps.

God Bless,
Bro. Ignatius Mary