Ideas from those that want to play architect

In that case, what comes to mind is sectioning off the East side of the main space, North to South, say 6″ to the East of the patio doors. Then split that space evenly from West to East and add a couple doors midpoint on the long wall. With the cubby split in two, you add ~ 3'x3' closets to what will be two rather small rooms ~ 6'x9'. Put a half bath in the gazebo where the grill is. The thinking there is that your sewage line will be easier to connect to the main bath's sewage line. Put the grill on the East wall adjacent to the sliding doors...unless it's a crawl space foundation allowing you to connect the bathrooms with the half bath on the East wall of the gazebo.

Short of moving the current kitchen - which I wouldn't do for cost reasons - and/or doors and windows and no loft, I'm out of ideas. I think putting the kitchen in the gazebo sounds like a good idea, but the resultant layout with an added two rooms plus bath on the main floor will result in an awkward common space.
Making the two rooms mentioned above larger will require moving the patio doors and Southern windows. You're still looking for a place to put a second bath if it's not in the gazebo. I lobby for a half bath in the gazebo as it can be close to the action and, I think, you don't really have any other space to play with. Your dinner guests don't all need to bathe or shower.

Here's an idea, cut out the rooms you want, to scale, from another sheet of paper and see what you can make fit on the current floor plan. Graph paper helps as you'll be cutting numerous iterations of shapes and fitting various door, window and furnishing scenarios.

Frankly, it's quite small (600sq/ft less the gazebo?) as is and doing what you wanna do is gonna be challenging if your intent is to not live or entertain awkwardly.

You may very well have to raise the roof. Don't put the second bath over the kitchen...bad Feng Shui.

 

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I didn't want to say it...but, yeah.