Hello, here are a couple of articles with some pictures that may give you some ideas:

https://www.dwell.com/article/rec-room-ideas-055f5aca

https://www.decoist.com/2013-01-21/rec-room-design-ideas/?firefox=1 

Try posting some inspsiration pictures for black leather sofas you like on Houzz so we can understand your style goal...farmhouse, mcm, boho chic, etc....the houzzers can help you fine tune the room.....

A fun rug or even put together some carpet squares. Maybe some poster art on the walls and some additional lighting. Table lamps if you want to use end tables or floor lamps.

Think of this as your great room, what would you do? Paint the walls. Area rug. Wall art. Floor or table lamps. Window treatment. Move the sofas a bit away from the walls and create a 8’ to 10’ conversation area. Keep 14” to 16” of space between seat and coffee table. .

At the staircase, add a column around the metal pole, add a hand rail on the open side, add wooden riser and tread at the bottom. Possibly add a stair runner down the staircase. Add sofa toss pillows and sofa throw. Add some potted plants or high quality artificial succulents.