Blackbeard's Devil Fruit hunt

Among the 4 Emperors, we have 1 Emperor whose crew has NO devil fruits (Shanks) and one Emperor whose entire crew has devil fruits (Blackbeard). Luffy's crew has a good mix. Additionally, Blackbeard is the only character in the verse who has two Devil Fruits, and he's actively looking for more Devil Fruits : Law's, Boa Hancock's, etc.

Question 1 : Why does Blackbeard need this much Devil Fruits when all the slots are litterally taken? Can he eat more than two, or can he share his secret to other crew members? Or did he plan to recruit more crewmates?

Question 2 : Isn't it weird that a pirate crew has litterally only Devil Fruit users? There should be at least one non-Devil Fruit user in case someone drowns. (I don't think Sanjuan Wolf can pick them up). So doesn't that mean that in addition to being able to eat more than one DF, Blackbeard is somehow immune to the Sea curse?