modal analysis of 7 storey 2D frame

you should consider modes till sum of mass participation goes more than 90% percent. in 2D models, 3 or 4 first modes will be enough (in most cases). Based on FEMA-356 beside of mass participation it is needed for modes with period more than 0.4 sec to be considered.

It depends on the properties you are evaluating. For example, if you are working on the influence of superior modes in the structure's response, it would be better consider more than three.