Also, is this request coming from the pastor?

Well, I'm new at this, so my opinion isn't worth a lot, but here's what needs improving where I'm at (which granted is an EF parish, so doesn't have some of the same problems)
1. Improve the choral sound: teach people to sing better, and get better singers.
2. Do more interesting/suitable repertoire, which means teaching the choir how to read music better.
I'd consider those universals. But "what else" depends on what Father says. I'd favor a Savonarolan Bonfire of the Missalettes, with a procession.

I thought I made that clear. It's all Father. But certain purely technical matters are givens, I think.

I am hoping to interest our parish in renewing a particular mass which is designated the family mass. it has had an attempt at a children's choir, which collapsed - they felt a practice during the week would be too much commitment, so it never really got off the ground. they have had various cantors and singers with guitars, who tended to just do solos, not a lot of congregational singing. everyone involved only did every second week so no continuity, or chance to build up repertoire. Also the mass itself was chopped and changed, leaving out readings, the creed etc. because it was a children's mass, and apparently children are not capable of enduring an extra 2 minutes from the bible (aargh). This meant that the really committed young families in the parish went to another mass where they could get the whole liturgy, and those who do go to this mass, the last of the morning, tend to be the less committed, more casual attenders. so again difficulties in getting anyone to do anything.
If ~I am given the chance here is what I will do for starters, the problems with dropped texts etc. having been fixed. Start a family choir, that is adults and children mixed choir. This means people with young children will be able to contribute and sing at the same time. Do it every week - continuity. Build repertoire.
Musically I would do the following - Entrance - choice of two hymns, from the sort of standard hymn tunes (Like 'Praise my soul the king of heaven etc.) By teaching hymn tunes, we will be able to change out the words, while still keeping the tune, giving a chance to build repertoire.
psalm, - something like a Chabanel psalm, sing the alleluia and its verse.
Offertory - a simple English proper, with psalm verses. This is something the children in my schola could work on as 'their' piece, it will get something from the propers in, and start to let the congregation become familiar with the antiphon/verse pattern, as well as the SEP sound. Probably choosing one antiphon for the whole season, with changes in the psalm verses. Encourage the congregation to sing the antiphon, the schola to sing the psalms.
Communion - during distribution: a Taize chant, focussing on one or two which can become well known. (Eat this bread, ...) As it becomes more widely sung, introduce SATB parts, and the voluntaries or verses, again building towards the antiphon/verse pattern. After distribution, a simple Eucharistic hymn of devotion, for the whole congregation to sing - go to piece would be Cead mile Failte, which is the only hymn at the moment they can reliably join in with. Add to this oh Sacrament most holy, and alternate them.
At the end - a Marian hymn (parish dedication to Mary) - probably go with Immaculate Mary to teach the hymn tune, and then vary the words from week to week.
Ordinaries - sing simple English settings for some parts, building slowly towards including dialogue (The lord be with you etc). Try to get the priest to sing at least sometimes (the priests rotate, we have one non singing, one who sings well, and one who could manage the simple dialogue chants if asked (pushed)
At the end of 12 weeks, we will have - some ordinary parts psalm and alleluia, two each entrance, communion chants, communion reflection, a variable marian ending, an sep offertory.
Next 12 weeks, I would build in another hymn or two in each of those places, including atattention to the liturgical season, ie Veni Emmanuel or such like. I would start to include an SEP during communion, again adding one seasonally, with the taize chants on alternate weeks, maybe an alternative marian hymn at the end, again trying to push the singing of the ordinary and the priests parts a bit further. I would also try to introduce the idea that sometimes the communion reflection hymn is something they listen to rather that all sing, paving the way for being able to do more complex pieces there in the future.
Sorry for such a long and boring post, just doodling my thoughts as I go....
I know this is all really basic, but you have to start somewhere.

Oh. and the plan to back this up with some family orientated catechesis at and around this mass, changing it from a children mass aimed at two years to a family mass aimed at supporting parents in their task of catechising their children, including liturgical catechesis.