Can we look to agadata sources to derive certain halachos?

Can a slave commit to accept the responsibility of a kesubah or is he unable to make such a commitment because he cannot own property?

Sources can be found here

If one gives an unsuspecting acquarium owner a predatory fish that he adds to his acquarium, is the benefactor liable for the fish that the predatory fish consume?

Sources can be found here 

If a fish store owner sells a customer predatory fish for his aquarium without informing him that they are predatory fish, can the customer demand a refund? Is the fish store owner liable to reimburse the customer for his fish that were eaten?

Sources can be found here 

What is the status of egg matzah as far as chometz is concerned and may it be consumed on Erev Pesach that falls on Shabbos?

Sources can be found here 

Are women Biblically obligated in the mitzvah of Sippur Yetzias Mitzrayim?

Sources can be found here