When booking the option to add luggage was not available and it was mentioned that this could be added later. After booking I tried to add luggage and it said it was processing this for twelve hours after which they said I would have to add it at the airport. After going to the individual airline I found that I can add luggage for less than half of what lastminute.com said it would cost but I'd have to do it with every individual airline and I would have to check in the luggage again at every airport. Upon checking other websites later I found out that you can add luggage for the whole trip if you just book through them and the trip is several hundred euros cheaper.
Update: More disaster!
While checking in for my flight (multiple airlines) I get the first two boarding passes without any problems. For some reason the third flight automatically gets checked in without me asking to do so. While the site of the first airline tells me to check in on the site of the other airline the other airline's website tells me I am already checked in but that they can't send me the boarding passes due to the booker having blocked this. I am now supposed to get off the plan. Grab my luggage. Buy luggage for the next flight. Request boarding passes at the airport. Go through customs again and make it to my gate in an hour. Avoid this booker at all costs!