I already have the wood railings
A picture would be very helpful.
Do you mean to enclose the porch?
If you use the rail as support, you could attach wooden window frame to it. Make sure the window will not be too heavy for the rails and that there is enough support for it under, by maybe adding extra timbers.
Before you install windows and enclose your porch, you may need to get a building permit. Check into that first.
Windows are made to set directly on 2 x4 's or 2 x 6's directly, but you need to add covers over the edges on the outside to seal off direct wind/temperature exchange. I have done it for a shed, but not part of a home, but it is not difficult.
thanks for the feedback, yall have given me a lot to think about