Could you advise how this space relates to the LR and/or kitchen as that might have an influence as to the look you might want to go with. If it‘s more of a hall/walk through, it’s going to need to feel connected.

For the dining area:

For under the stairs, design a storage, serving area for your table.

As for the wall between bedrooms, a full size mirror.

How many people at the table?
What are the measurements of the dining area?

I would suggest bright colors: cream, white, slate blue, sage green and silver
And metals in soft tones: silver, brushed nickel, mirrored finishes

NO to a lot of black here. But dark wood is fine.

Depending on how many people will be seated, you can do a large square table or slimmer rectangular table.

An example of the layout of furniture you can use in this back wall

Another option if you dont want mirrored or silver touches

Not sure how much space you actually have with knowing dimensions so I’m showing this with four and six chairs. You could use a console under the stairs or do custom built-ins.

I'd go with Warm Modern - Wood & Earthy Tones!