New Lens or New Body?

Sorry I mentt to write 18-55, big differthinking

The reason for the FF 5D is due to the fact that I take portraits most and my only EF-S lens is the 18-55... Ilooked at the 7D but would like to go FF at some point that is why I don't really want to buy the 17-55.

The reason for asking is because I notice when I take portraits of my kids it can be very difficult to stop blur without lifting the ISO too highland getting grainy images! As I said Denmark isn't always the lightest of countries...

Wouldn't the 24-105 overlap a lot with my existing lens on a crop camera?

Why not 17-40 on a crop?

Thanks for the advice!