In principle, QlikView does not care about cardinality. Whether a link between two tables is a many-to-one or many-to-many relationship is irrelevant to QlikView. QlikView works the same way in both cases.
But having said that, there is a place where where it does matter: When showing frequency for keys in List boxes. Then QlikView tries to identify a table as the one where the key is a foreign key so that this table can be used to calculate the frequency.
About memory calculation: it is not just difficult - it is impossible.
1: The data model takes place. Proportional to number of rows x column in data table,
2: Symbol tables take place. Proportional to number of fields and number of field values (cardinality)
3: Every chart takes place. Proportional to cardinality in Dim1 x cardinality in Dim2 x cardinality in Dim3 etc, Further, if the calculation implies fields from several data tables, even more memory is needed.
Bottom line: Make test application and extrapolate.