If you are talking about having one room along a side of the house have screens (and just one wall with screens) instead of windows, my parents had a porch like that. You will not get much fresh area flowing into the porch because with three solid walls you won't get a cross breeze. A screen porch works best, in my opinion, if it has screens on two walls so that you can get a cross breeze. My parents ended up converting that porch to a regular room and adding on a conventional screen porch that had screens on 3 sides. If you do it, make sure that you have adequate overhangs over the screen and that the floor slopes slightly to weep holes for the water to drain out as you do not want to have standing water from rain storms, snow melt, etc. in a room over a basement.

My opinion would be to stick with the character of the rest of your house. If you have Coastal and Craftsman features, don't go too Contemporary or Formal. Both examples that you have posted. ;) Besides the siding on the outside of your home, do you have any hard surfaces, like brick or stone? If so, match those instead of bringing in a third element. We recently built an outdoor area for our home. I had my heart set on a stone fireplace, but the house is brick and stucco with a wooden screened porch. The more that I thought about it, the more I decided that bringing in another element was too much. Matching brick would be the way to go. I am so happy with my choice. We also have columns that mirror the columns on the inside of the house and painted to match the screened porch trim and stucco accents. A cedar wood pergola is stained to match the darker taupe of the majority of the stucco. All colors blend in with the brick. If your house is all siding, then I would go with the stone. for inside and out. I believe that the plaster both outside and in, as shown in photos 2 and 3, would be too contemporary and formal for your home. I like the interior stone and wood trim photo that you posted with the hearth, but sadly, you do not have room for that set up. Another opinion...I'd take down the knee walls. You don't need them for a division. The one between the window is taking up valuable wall space. You can create a natural division between the dining and living space with your furniture. I know from experience. We put a built-in in our living room, and I wanted it to have some character, so the middle section sticks out about 10 inches beyond to side sections. That middle section has become a thorn in my side and prevented a couple of different seating configurations that I would have much preferred in that room. The bump-out gets in the way. I think that your knee walls will narrow your walking space, getting around furniture, such as a sofa. Again, just my opinion.

What a beautiful room! What kind of floor is this?

I understand the carpenters point. The posts are spaced equally and look fine from the street. None of the posts block or impede the views from the windows, which seems to me more important than the situation with the door. Maybe the previous owner had a hard time waking up and needed a convenient support as they left the house for work or returned exhausted in the evening. A good story can sometimes enhance a design feature.