Why did Chazal choose Arami Oved Avi to illustrate the Central theme of Exodus in the Haggadah as opposed to - for example - Parshat Bo?And given that there is a Tosefta (Peshachim 10:8) that states: "Those who live the in the city and have nobody to recite Hallel would gather in the shul".
How would you know how to lead a Seder without knowing how to lead Hallel?
Here is a proposed answer to the 2 questions
Originally, all farmers, when they brought the Bikurim, the first fruit, would recite Arami Oved Avi. So Chazal chose Arami Oved Avi to explain the Exodus because every farmer in Israel would be familiar with Arami Oved Avi when they brought the bikkurim annually to the Beit Hamikdash in Yerushalyim.
Now we can answer both questions because we can now explain:
1. Why Hazal specifically picked this Parsha over any other
2. How a Leader at the Seder could be familiar with the Haggadah [Arami Oved Avi] yet still not be familiar with how to lead the Hallel