You can find a YouTube playlist here with many of the songs suggested below.
Gathering
This week is the first appearance of John the Baptist and so it would be very appropriate to use On Jordan's bank, the Baptist's cry (CH 334 / MP 538). The cry of "Prepare the way of the Lord" is also a strong text for gathering and Prepare ye (YouTube) from Godspell would make a great introit for a choir or band or could be adapted into a call to worship. You could also pick up this text with more congregational songs such as Prepare ye the way (CCLI), Prepare the way (CCLI) or Prepare the way of the Lord (Hymnary) which can also be sung as a round. Some more general advent hymns would be Hark the glad sound! the Saviour comes (CH 277 / MP 210), one of the traditional Scottish paraphrases, or Alleluia! Hurry, the Lord is near (CH 280).
If you are using an Advent candle lighting song then Christmas is coming (CH 282 / CP 34) and Advent candles tell their story (STF 165 / link) are good options for the pattern of Hope, the Prophets, John the Baptist, and the Virgin Mary, while Hope is a candle, once lit by the prophets (CH 284) and We are a people of hope (Hope) work well for the Hope, Peace, Love, Joy themes.
Word
You might like to use a short Advent song before the reading of scripture. This is a good opportunity to give some musical continuity to the season, either by using the same song each week or by using songs in a similar style. The following songs all have a similar text, praying for Jesus to come, but use a mix of English, Latin and Aramaic: Maranatha (MV 19), Come, come Emmanuel (link), Veni, veni (WGRG), and Veni Immanuel (WGRG). There are also some settings of plainchant which can work well here as continuity through the season, with the simplicity of the music allowing an opportunity for the power of the words to really sink in. The Advent Prose (NEH 501) is widely sung throughout Advent while O heavenly Word of God on high (NEH 2) would be another option.
The setting in CH4 is the wrong verse of the psalm for this week but there are a number of well known hymns inspired by Psalm 72 including Hail to the Lord’s anointed (CH 474 / MP 204) which has alternative versions by New Scottish Hymns (New Scottish) and Indelible Grace (link) and Jesus shall reign where’er the sun (CH 470 / MP 379). O God, with holy righteousness (WGRG) is an excellent setting of a Genevan Psalm tune which could also be sung to Forest Green while Christ shall have dominion (Grace) which is set to a tune by Arthur Sullivan which is associated with “Onward Christian soldiers” and the marching feel actually fits the tone of this psalm quite well. If you prefer to sing the psalm responsorial then In his days justice will flourish (PFAS 72C) is a good response to use.
Response
If you didn’t use it as a gathering song then On Jordan's bank, the Baptist's cry (CH 334 / MP 538) is an obvious link to the Gospel. The songs suggested above focusing on the call to “Prepare the way of the Lord” could also be considered along with the more reflective Wait for the Lord (CH 276). Lo, in the wilderness a voice (NEH 170) and Wild and lone the prophet's voice (STF 189 / Hope) both take the lone voice in the wilderness as their starting point, asking what that should mean for us while Through the prophets (New Scottish) also focuses on John the Baptist. When out of poverty is born (CH 291) could also be used with it’s repeated call of “prepare the way” at the end of each verse. When John baptized by Jordan's river (Hope) would give a more explicit focus on the second half of this passage.
The Epistle would link well to songs about living in harmony with one another including well known hymns such as In Christ there is no east or west (CH 624 / MP 329) and Brother, sister, let me serve you (CH 694 / MP 1261), the worship song We are one in the Father’s love (CCLI), or short songs such as Ososo / Come now O prince of peace (CH 275) from Korea, Dear friends, we’re one (STB 311 / Hymnary) from Laos, or God welcomes all (WGRG) with words set to a tune from South Africa.
Isaiah the prophet has written of old (CH 241) is a lively song which links strongly to the Old Testament passage. The classic Advent hymn Lo, how a rose e’er blooming (Hymnary) would link to the opening verse as would Now the heavens start to whisper (GIA) which can be sung to the traditional Welsh tune Suo Gan. All over the world the Spirit is moving (MP 18) links directly to v.9 while some of the language from this vision is picked up in O day of peace that dimly shines (Hope) and We dream of a turning (GIA) which can be sung to the Scottish folk tune Loch Lomond.
Sending
You could finish with songs about our longing for the better world which will exist when Christ comes such as Come, thou long-expected Jesus (CH 472 / MP 102), Christ is coming! let creation (CH 475), Hear the call of the kingdom (MP 1282 / CCLI / Getty) and Waiting here for you (CCLI). Long ago, prophets knew (STF 178 / Hymnary) picks up the theme of the prophets but looks forward to the end of the Advent journey. May the God of hope go with us every day (CH 256) is worth considering for a blessing song as it links to the words of the Epistle.