The translator! And the experience of Torah reading in shul, back in the day. Noting that skipping text in a Torah reading was iffy... Plus, how the person who will lead the prayer connects to the person reading Haftarah. And what is the etiquette for reading the Torah, for leading prayer, for duchening (if a kohen). And what about a blind man? Also, the prohibition against a kohen with blemishes, especially, but not only, on his hands, going up to bless the congregation. Plus, other impediments blocking participation in various ways. Also, the danger of round tefillin.