This is the 02 Design which i thought would be worth posting for people to get an idea of how you can make a simple home with 2 x 20ft containers. As you can see its functional but also there is a lot of wasted space that could be utilized but it still fits!
For an example of how to work things out generally I would go for the number of people living in the house plus one when it comes to seating. As there is only a double bed in this house and living room seating for 6 you can half that space. Dining table could be set for 2 with a fold down table so that more seating could be added if needed rather than taking up 1/4 of the home. Sofa bed or Murphy bed would be more practical than a double bed that looks like its stuck in the middle of the sitting room. Not an ideal plan for me this one but at the same time like I said its all in there and with excess. If creating open plan in the sitting room/bedroom I would go with a divider after reducing the amount of seating as this will allow wardrobe space in the bedroom and a TV unit in the sitting room as well as small storage.
But the important thing is here is you can see how it can be done at the same time having a canvass to work from you can also plan out how you would do it.