Hi Lauri,
Keep in mind that you can chose destinations yet leave the ticket open dated. I only decide on the first date, then leave the rest of the ticket open dated. It's very easy to get the flights as I need them.
I'll leave it to others to advise you on whether you are better off chosing a possible 20 segment itinerary to then reissue as needed, or whether to ticket fewer sectors and add as needed.