Wherever you first put furniture you will likely move it, so don't worry to much now. As far as warming it up the obvious thing is to add colour to the walls- you could get a wall paper to add pattern. Short term you might just prefer to get a rug.

I’d keep the layout as it is, especially if you’re in a budget. How great to have the kitchen area there your guests will love you! I’d get a large rug, a comfy sofa bed (on the wall with the chairs on) and a large storage unit (ikea?) for the opposite wall, also for the tv

The bed in the photo with a solid surface under the mattress looks like a better option than a sofa bed. Sofa beds have "the bar" that is uncomfortable to sleep on.

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