First, you are so luck to have such a wonderful getaway vacation home! It is on a beautiful lot. I agree with missymoo as well, and also what Olychick said. Something about that table smack dab in the middle of the room seems to block entry into the screened porch. I love the idea of a sofa against the wall, something like what robo posted with some comfy cushions and arms, and a chair for reading with a footstool that could also double as an extra seat. Add a small cocktail table you can also use for a tray of snack food. The bar cart is also a great idea. Encourages people to gravitate to where the food and drinks are. You could also string up some lighting along the perimeter and it would look very inviting. Do you get a lot of sun on the deck? It looks shady so I would think a new round table with chairs for seating would be fine and then move your grill & the pub table out there. You can get some pretty nice chairs that swivel and rock. I have also seen some benches that double as storage for the cushions so that might be an option if there is room. That would keep cushion maintenance down for you when you aren't there.

Any photos? What did you decide to do?

I'm not trying to waterproof the floor. :). There's no grout in those pedestal systems. The water flows right through to whatever is beneath. I suggested the porcelain as a nice floor for a deck as a non-water proof deck refacing or for above a complete and correct flat roof system, not tiled to the membrane (which I wouldn't even do with schluter), and I recommended the translucent panels as being nice on a second story deck above another to serve to let light through. Rain will blow onto a screen porch. You don't want to trap it. I would definitely have to have solatubes or skylights above to make the translucent panels worth anything. I think some of us are seeing a dry screen porch at the basement level, some are seeing a "wet" screen porch at the basement level (me, first read through--then I wasn't sure), and some of us are seeing a dry screen porch at the upper level (my second guess). And people are recommending flooring either to make the upper level nice or keep the lower level dry. So this whole thread is a mess. I think OP just wants a nice--not waterproof--floor for a second level screen porch which just happens to have a basement beneath.

Why not just do IPE IMO a great real wood instead of fake