When I make T-shirt quilts I start with fusing the stabilizer onto the T-shirts then cutting out the logos, decals, designs. I leave a fairly large amount around each one- figuring I will square them up, determine size& shape as I go along. Then when I have them all cut out I take them to my bedroom & start laying them out on my bed, rearranging, moving things around until I have a layout I like. ( I do have a design wall, but have found using the bed easier for T-shirt quilts. ) one I have the layout I like I start measuring, figuring out what I need to do to make things fit together. I often work in sections, trimming, sewing a section at a time, laying it back out & creating the next section.
Last one I made was actually a hockey Jersey quilt- boy, it was a job! And a heavy quilt. The recipient loves it though.