Is church attendance and/or participation in Communion a requirement for Roman Catholics? Is church attendance and/or participation in Communion (i.e., Lord's Supper, Eucharist, Mass) considered a requirement for Roman Catholics?
Attending church on the Lord's Day (Sunday) and other holy days of obligation is a requirement for Roman Catholic Christians.
According to the Code of Canon Law (CIC) 1247 (cp. Catechism of the Catholic Church (CCC), 2180),

On Sundays and other holy days of obligation, the faithful are obliged to participate in the Mass.

Frequent participation in the Communion (i.e., Eucharist, Lord's Supper) is encouraged, as long as the pre-requisites for participation are satisifed (CIC, 912-923).
According to the Code of Canon Law, 898,

The Christian faithful are to hold the Most Holy Eucharist in highest honor, taking an active part in the celebration of the most august sacrifice, receiving this sacrament most devoutly and frequently, and worshiping it with the highest adoration. In explaining the doctrine about this sacrament, pastors of souls are to teach the faithful diligently about this obligation.

In particular, Roman Catholic Christians are obliged to participate in Communion annually.
According to Code of Canon Law, 920 §1-2,

§1. After being initiated into the Most Holy Eucharist, each of the faithful is obliged to receive holy communion at least once a year.
§2. This precept must be fulfilled during the Easter season unless it is fulfilled for a just cause at another time during the year.