I think you have got their
Hanging the two front boards loosely will help you to assemble the four boards that you are currently working on, but have you realised that you will have to do this for the complete layout all the way along it's length, every time you assemble/disassemble the layout
I don't think doing it the other way, splitting the boards across the layout is a possibility due to the type of legs, you would have to start at one end taking off the front and back boards together, but then their isn't the legs to hold these two boards up whilst you part them
Regards
Geoff