What a nice sunroom. I like the cushion, but the whole thing still seems rather bland on my screen (no views to pick it up). And I've always been a white lover. My "vote" would be for you to choose a color scheme and then paint the wicker a glossy color of your choice. Maybe take a cue from that nice brick floor so that any choices make it look its best. I'm thinking a dark brown or very dark, slightly cool green, but glossy navy sounds wonderful. :) Red? You have so many options, depending on what you like. I think it might help to split up the furniture, though. Maybe put the chairs and ottoman on the end of the porch for a separate seating group, facing each other entirely or angled also back toward the main group, and then bring in chairs of another style to go with the loveseat, turning their backs, at least partly, on the garden (swivels?). All the wicker wouldn't have to be the same exact color. Maybe only the settee in a dark color and the chairs in a lighter version of the same color, or vice versa? The tables could remain to flank the settee, painted the same color, to add importance to that area. But maybe cover the tops with something a little different to add more interest without actually grabbing attention? It could be a different material than glass. Or something attached to the underside of the glass (collages from school papers, antique-style maps, fabric with a great pattern, seed packets relating to the garden, whatever furthered the look you like). Will you need a reading lamp? Floor lamp, or the coffee table could become a side table to hold one. Not right now, maybe, but how about upholstering the top of the coffee table to turn it into another piece to sit on, and in the process break up the expected? Or move it to another part of the porch altogether and set plants on it?

Post a picture and extend the HVAC duct to the lanai if you plan to keep the doors open or your AC will never turn off.

Our floors were open to ground also. We had foam sprayed in from the underside. In some places, where it was a tall enough crawl, we had pink stuff, foil covered foam installed under the floor joists, taped and touch in foamed along edges. We did get occasional leakage between boards, once peeled out, ya don't even notice.

I agree that the ceiling feels heavy. White would definitely make it feel more airy. You may also want to explore the option of doing something fun like picking up the blue color in the chair.