I like the bottom two pics. why not copy those?

if not brick, get a piece of marble or granite for the hearth and inlay it,

or raise it up a bit. up to you.

here's two other corner FP

With so many decisions to make I would for sure hire an interior designer. You give them the ideas of what you like and they will come back with a plan. You can execute the plan yourself or hire them for more help

You build up the hearth, but the fire box has to go up as well. If it is gas, depending on your building code, you may not need a hearth. Much sleeker looking.

https://www.houzz.com/discussions/4229033/decorators-opinion-on-gas-fireplace-no-hearth-ok

Either do a flat hearth or an actual raised one. Do not do that tiny toe stubbing hearth that will cause accidents.

Contemporary Modern It all depends on what color blue you're looking for. Try them out in the room and work off the colors in the rug you select.

I made your TV larger in the image.

Blues are always tricky too light they look like a bay room so maybe if you love blue go dark or a soft green like Healing Aloe from BM I often cut it 25-50 for just the right shade . It goes with everything a true neutral IMO. I would not do a hearth if it is not needed for code what mess with all the same floor and no tripping hazard. Too bad you had to keep the corner FP but oh well.

With the fireplace wall angled, a floor hearth rather than a raised hearth is a better option imo.

What you’re describing usually lands closer to “soft modern” or “organic modern” than coastal. Muted colors, calm vibe, no beach stuff. Coastal modern just gets slapped on anything blue these days.

And yeah, agree with others, don’t do the weird half-inch toe breaker hearth. Either flush or commit to a real raised one.