Consider planking the ceiling that goes up at an angle - they make vinyl planks that are lightweight / made for the ceiling - in white, in a woodgrain - really adds a lot of beach vibe without a lot of expense. You could select a very wide pale gray washed driftwood vinyl plank element and continue it horizontally all the way down one (ideally exterior) wall to evoke original beach cottage siding / add texture and get the tonal look you seek. Your existing floor looks great for beach cottage, it could even be whitewashed or gray-washed if you are bold.

For the 8' ceiling, I love the suggestion to paint it a softer shade of the wall tone. Other elements that really evoke the beach - burlap, coir or rope wrapped elements, baskets, wicker, chinese bamboo furniture, sisal rugs, and lots of painted wood (i'd go thrifting for the furniture you need, then paint and distress them). Anything that looks like natural driftwood with a bark edge will advance this look.
Take the existing light fixtures and work them over - change out paddles to be floor wood tone / wrap the elements with rope and hot glue for flair. Dining could use a "found chandelier" spray painted dark teal or navy rather than the dark bowl i see.

Set a color story (aqua, kiwi green and khaki/stone) for instance, and then use different tones of these colors in every selection you make. Buy craigslist furniture that has good bones, and paint it in tonal variations on these colors. Select one colorful print fabric that guides your color story - if you look at a paint color chip next to your fabric inspiration and it looks good, you can use it on an old piece of furniture and know it will layer in well.One thing to be cautious about is your blue color family - blue-green / turquoise is more classically "sea" blue than indigo / navy / cobalt. Whatever major color story you start with - use that in muted tones on the walls, stick with that color family as you add blue things. You can do a room in blue greens and add one or two cobalt accents at the end, but if you mix all the way through you won't get the look you want and you won't know why it doesn't work. To mix true blue and blue-green aqua, you realy need a strong patterned fabric that brings them together well - it is better to settle on one and stick with it for a deliberate look.

Black leather is not beachy, but you can always cover it with a gray, khaki or off-white(stone) slipcover until you go a different way - slipcovers are very beachy and very practical.