Thank you for this suggestions and inspirations like starting the trip in a different city than I live or adding side trips.
As this "side trip" can be just another trip that I could plan even a few months after finishing the first one. There are some limitations that I noticed while playing around with *A RTW tool, for example I can't go back to the same continent that I visted once, as I tried eg. adding "side trip" to BKK like this:
FRA-SFO-TPE-VIE (as there is a good direct BR flight from TPE to VIE, and it is easy to come back to WAW from VIE too). and than WAW-IST-BKK-DPS-home but it did not allow me to add BKK... Only Africa was available, this is why you suggested CPT?
And I also noticed that I would need to calculate miles very carefully if I want to achieve what I want too.
How is it possible that building the ticket as RTW would be cheaper than doing the normal Round Trips, is it like a special fare or how it works?
And also... I have no idea how to book it, the *A tool is a bit too limited for my case as it does not have one of the airports I need to fly to...