You should consider "works like" and "looks like" prototypes (which may correspond to back-end and front-end here, and a thin "spike" all the way through ASAP.

You should consider "works like" and "looks like" prototypes (which may correspond to back-end and front-end here, and a thin "spike" all the way through ASAP. In other words there should probably be a number of shards tackled at once to help ensure that you haven't omitted something critical from the design.