i have to make crab cakes for about 55 people how much lump crab meat do i need to make sure they are nice and meaty?

How are these supposed to be part of the meal? An appetizer or first course, part of a buffet or entre? That detail certainly needs to be delineated before you can decide on quantity.

Have you made the crab cake recipe before? If so, how many cakes did the recipe make, approximately? Simply take that number and do the math to feed 55. If your looking for "meaty" cakes by a bit more than you calculated to be safe. Cooked crab cakes can be frozen (I use parchment squares to separate each one and wrap individually with saran wrap & bag before freezing) and best defrosted and reheated in a skillet and eaten within a month or so, IMO.

See chef-menus.com which has a great chart showing amounts needed of various foods, for serving 50 or more people.

Here's one option for you that makes 12-14 little crab cakes, that could be scaled up as needed: https://food52.com/recipes/18201-brigit-binns-crab-cakes