Houzz has good articles: "In this dining room, the splashes of red in the canvas are echoed in the dining chairs, making the space feel cohesive. Notice how the rest of the furnishings are neutral, proving that you don’t need to use color everywhere to make a statement."

https://www.houzz.com/magazine/decorating-101-how-to-choose-your-colors-stsetivw-vs~28100106

Hillgrove Project · More Info

{Just like the red above] you might like repeating your blue. You could experiment with art, picking a color from a large canvas art piece; the art might have a workable color palette in it

Maybe you'll end up painting the island in a neutral color. Blueberry dining room. ;)

https://www.houzz.com/products/blueberries-canvas-wall-art-by-emily-drummond-30x24-prvw-vr~75876586

Already have an I guess mid-century light - this looks like a crumb collector to me, but could work. 82" wide, and nice to have sofa that has a good look from all sides of it...?

Armen Living Phantom Mid-Century Modern Dark Gray Linen and Walnut Sofa LCPH3DG · More Info

https://www.houzz.com/products/phantom-mid-century-modern-sofa-walnut-dark-gray-prvw-vr~102525213

Decide what your focal point is. It can be a piece of art or your view. Face your sectional towards your focal point. Regarding color, I would stick to a neutral and monochromatic scheme, multicolor, or go with a few bright colors to build on your bright blue (add possibly bright green and bright purple). You will probably have to "float" your seating arrangement in the middle of the living room. What I mean by that is get a piece of paper and draw a floor plan using measurements of your living space. Then cut out of paper your sectional and any other pieces of furniture you'll have. Place the paper furniture in your floor plan. You'll probably have to move the furniture in the floor plan several times until you find an arrangement you like. This is not set in stone. Put your sectional on furniture sliders so you can move them around easily once you get this plan onto your actual furniture. Regarding the entryway, you'll have to fit that into your plan as well. You could have a runner to define the entry. Also, (if it'll fit) you may want to have a very narrow table, lamp, and mirror for the entry. Don't forget about lighting. That's often an afterthought in peoples design plan. In my opinion, one can never have enough lighting (especially in the kitchen)! That being said, in a living room, here is what I think makes the best atmosphere: one table lamp or wall sconce in each corner at chest height. Can't wait to see the result!

Rug could have grey and blue --sold in 41 colors --

Apt2B Marco Sofa, Smoke · More Info

https://www.houzz.com/products/marco-sofa-smoke-prvw-vr~82936618

Stop thinkg sectional and go sofa and 2 chairs a much nicer comfort level and a lot more adaptable to other spaces or even just to have a change once in a while. BTW if you reall y want help we need a floor plan to scale with all measurements clearly marked along with windows and dooraways.Also proper pictures not realtors warped ones.