We enclosed our previously screened-in carport, placing two small conventional windows on the SW side, facing our tiny sideyard. Both the SE side (facing our back garden) and NW side have sliding glass doors, the NW doors having glassed-in miniblinds. Both sliding doors have thermal drapes that can be used to cover them completely in weather that is too hot or too cold, and I have both a portable dehumidifier in the SW corner and and a large "end table" automatic quartz heater in the NW corner. I placed three large area carpets over the concrete slab, giving me essentially three different areas in which to arrange things. The slab absorbs both heat and cold, so if I am attentive to the room's needs it is entirely possible to keep it comfortable year round by adjusting the drapes, ventilating, and running the dehumidifier and heater. My sliding glass doors are screened, so on a good day I can open the doors at both ends and have a wonderful breeze through the entire room, and almost have the look and feel of a sun porch *and* a screened in porch, but without the inconveniences. The NE side opens into our tiny dining area, and we have an air conditioner in there. On very hot, humid days, our "sun room" is cooled sufficiently from that and a ceiling fan we added. This is a fairly low cost solution for anyone with a roofed-over carport or garage that they never park in; it's incredible the amount of living space that can be added to a home--it's now the largest room in the house, and the most attractive in terms of view, lighting, and general comfort.

Unless you rectify the water issues in construction aspects of the porch itself, the sustainability, longevity, and maintenance of any flooring flooring system and associated area construction will be in question (just like your wood floor and columns)unless you choose a system specifically made for an exterior application. With your porch in its current state, what comes to mind is a ceramic/stone solution made for an exterior application with membrane over mud-bed over menbrane construction and a drainage/gutter/flashing system (like at least Schluter Ditra/Kerdi or even better Troba/TrobaPlus with a BARA/BARIN drainage/gutter systems for porch/terrace/deck systems). as for tile product choices, a high quality porcelain is an excellent choice for decorative exterior applications. a high grade masonry sealer for the joints is advisable as well. The important thing here is to either: (1) fix the water coming in, or (2) use a system where water penetration is irrelevent. Please dont make the mistake of simply installing cement board and tile over the wood substrate to save costs. While it may last longer than the wood, you will still most likely get water penetration into the wood subfloor/framing system, which in time, will still deteriorate the underlying wood, eventually causing tile/backer board system failure. Nothing will last over a wood subfloor system over wood framing if you dont take the proper precautions. Here is a link that might be useful: Schluter Systems

windows would not be installed directly against a column they would be installed in a framed wall.

I think you the rug size you show in the mock up works - you could go larger but then there's that rain thing although if you get the blowing rain like we do, it will get wet regardless. I think a smaller rug for just the seating area is going to look skimpy. As for the throws..... Cheryl and I will not make this easy for you - I say 1 or 2 !! And I love water sounds - this is a small section of our creek although it's hard to hear from our porch until it turns into a rushing river with the storms we get!