Field lengths don't actually save you any space, so just use the text type in postgres since varchar(200) or whatever is just a constraint that makes sure you don't but any strings that are too long into the field.
Primary keys are not really a thing, it's simple sugar for:
- Making an index on field
- which is a unique index
- and is restricted to not null
are not a thing in postgres despite what Andy says, they are called functions in postgres