All of the above
Sample size is critical in examining characteristics of a particular population. Generally the larger the number in the sample, the higher the likelihood of a representative distribution of the population.
Total population should be considered because a sampling from it is a purposive technique that examines a population that have a particular set of characteristics.
Generalizability is the degree to which research results conducted on a specific study to groups can be applied to the population at large. This will reflect the characteristic of the group.