Dropsy, you have quite a few options. Since you don't have to worry about the foundation, floor, or ceiling you can can concentrate on the screening. You can make screen panels yourself to fit between your existing columns (not my favorite option), you can purchase screen frame kits (aluminum frames and screening) custom made to fit your measurements, you can purchase a 'walls only' screen kit, or if you like the idea of creating creating a three season porch, you can purchase screen porch windows (this is a neat product). You should also consider screening in part of your wrap around while leaving some of it open. If you are intent on screening the entire porch, investigate the screen porch windows option. We cover these and even more ideas on screening your porch on our website (too much to cover in this space). Hope this helps.

Here is a link that might be useful: Screen Porch Design