Q: How to add national holidays to calendar?  

A: You can import holidays as iCal (.ics) calendar which could be downloaded from Internet. You could start searching from our iCal's download page: http://www.essentialpim.com/?r=download&pr=ical

Q: How to generate a list of upcoming birthdays and/or a list of all birthdays.  

A: You should switch schedule to Table view, filter tasks according to Birthday (Holiday) category and set date ranges. You'll get your list then.

Q: Is there a possibility to make a text search, among all tasks scheduled in the current period?  

A: Yes, switch to Table view, then you can make search by keywords then set date limits.