Not really an answer to the paint question, but something else to consider.

Many BBQ restaurants in Texas install full-window garage doors in outside walls (about 2/3 height, on top of a short wall), with the horizontal tracks hidden up above the sheetrock ceiling. When you roll the door down you only see the windows. When you roll the door up you have clear space and can only see the metal tracks on the sides. Its hard to hide the metal tracks completely, but it certainly makes the conversion from closed to open very easy (just roll up the door).

Bruce

Thanks, Bruce. I'll check into this. We do want screening in the summer to keep out mosquitoes.

You might like something like this.

Here is a link that might be useful: screen/storm

Be VERY careful with the orientation of the space for sun and your location in the country. I just eliminated one of those ovens attached to the house! It was on the south side of the house, and the "convertable" windows trapped all of the heat. Not that being outside in the south in the summer was all that doable to begin with, but when the space was 140ð, it held on to a lot more heat through the cooler evening hours than it would have without those windows. Yes, with them raised to allow the screens to let in air. With the glass completely removed, it let in too much water when it rained. Even for the cedar framing that they used. It rotted. Which was another reason we eliminated it.

If you are in the North, the room will not be a 4 season room without some type of heat. That means insulation, and good enough windows to hold on to that heat. That rules out removable windows of any kind, as they are mostly very poor quality and compromise your building's envelope.

4 season rooms are only practical if you spend a lot of money to actually create them up to the same standards as the rest of the house, and climate control them. Otherwise, you're better off with thinking of it as a 3 season room, location dependent on what those 3 seasons might be.

I am looking at ReliaBilt windows at Lowes. They are made so the windows come out for cleaning - I will be taking them out and leaving them out for the summer. I will certainly be careful about buying windows with the correct heat gain coefficient and U factor.
I am concerned if I do not completely take out the windows, I will still get too much solar gain in the summer from the south facing windows.
As to water entering the room:
The north wall is the original house wall so there will be no windows there.
The east wall is beside a covered porch so no rain will enter there.
The south wall could be problematic for sun and rain. I am hoping to minimize these problems by having a 2-ft roof overhang and then running an 18" awning type porch valance across the overhang.
The west wall will also have a 2-ft overhang. These windows will have awnings to help protect the interior from sun and rain.
I do plan to fully insulate the room and to use a direct-vent gas stove to warm it in the winter. I don't plan to cool the room at all. I will install 2 ceiling fans (the room will be 16 x16).
I live in the mid-atlantic region.
I looked at the Harvey Industries system, but they are not located near me.
I plan on having a regular foundation.
I appreciate all the comments.

To answer your question about useing exterior grade products indoors,should be fine. What do you call "a regular foundation",concrete slab or raised wood floor? I wouldn't paint either,opting instead for tile,flagstone,colored concrete,coved sheet vinyl or similar. Double hung windows with both upper and lower movable sash is perfect. The key to keeping the room from getting hotter than ambient tempature is proper ventilation. With open windows and openings at highest point in room,passive airflow will prevent heat being trapped. During unusualy hot weather an exhust fan at top of room may be nessary. In a perfect scenario one or more deciduous trees would afford shade in summer and allow sun in winter. Trellised/arbored vines are a close secound choice. Check out a site called build it solar for ideas on useing the room as a solar heat collector for suplimental home heating. Carfuly research roof desighn,esp pitch. If your home's roof runs water onto this room,a shed roof is a terriable option.

Thanks for your input on the exterior grade products. My foundation is a concrete footer, block, then a wood floor.
I like your idea of a fan! I would love to have deciduous trees but the placement of the driveway and septic tank/leach bed would make that difficult. The trellised/arbored vines are a good option though.
I'll be checking out the build it solar website for ideas.
Thanks for your ideas and comments.

The Gristmill Restaurant in New Braunfels, TX has dining rooms that are the ultimate 4 season rooms. You cannot tell it, but the windows do have screens that are fixed and the Windows open out. It used to be an old Mill, so all the massive beams give it amazing character. This is my idea of a perfect 4 season room, on a smaller scale, of course, for a house. These rooms are huge.

You're right. These rooms are beautiful and the perfect screen/4-season room. It is great the windows open out instead of sliding up (as a double hung window does with the window partially in place still resulting in solar heat gain). I will look at windows locally that open out instead of up.

I'd be very happy living in that dining room LOL!

When I built my porch I used 1x4 T&G mahogany and finished it with Penofin. I'd rent a large orbital sander every three years or so and lightly sand it and re-apply the finish. I graded the floor to drain to the outside and not hold water. For the interior walls I took 1x4 square edge mahogany and re-sawed it to about 5/16" thickness. I laid it up the walls interior walls.I cut 1/4-3/8" strips that had a rough cuts from the bandsaw and alternated those steps with the 1X4 going up the wall. It gave a nice texture. I was going to have window inserts built but never got around to it. It was the nicest room in the house and was instrumental in the sale of the house. We miss that room! There is a lot of stuff that people try to pass off as mahogany today. We used good consistent color material. We painted the window sills and trim some shade of white. It was a great space.

Jackfre, your mahogany sounds like it was beautiful and served you well: both while you owned your home and when you sold it. I'll look into mahogany prices and see if it is an option.