Are you thinking each person in your group would design their own block? There will be quite a variety in the results. An autograph quilt would make it very personal, and non-quilting members should be invited to participate.
If you are not familiar with the "Prayers and Squares" project, you might like to visit their website at prayerquilt.org for ideas. Although their emphasis is on making quilts for people with illness or tragedy, the concept of whole congregation participation might apply to your situation.
Best wishes on the project -- your paster is blessed to have members like you in the congregation who care so much for him.