Bryan, Chris thank you for your help! It ensured me that there's no golden rule for this problem. The problem is, that I'll need people to add quite boring data (e.g. demographics, car and real-estate conditions).
I'm considering to split it up somehow and slowly but surely make people submit all the needed data. Capturing an email address and then guide the users through a personalised program making them fill everything, seems reasonable.
I was just surprised that I hardly found anything in this topic on the interwebs. Maybe I'll write one our of this case.
