[villagetinker]

Assuming you have done your homework with ARC for approval, you might consider:
If this is actually a lanai expansion and being enclosed, it is my understanding that there are specific requirements for additional electrical receptacles, also, when I looked into this in the past (a previous thread), there were DIFFERENT requirements for floor height based on the original house construction. I called the building department, and spoke with them for almost 1/2 hour and was more confused then when I started, but I had at least an understading of the questions to ask going forward. Removal of the sliders gets into this also, and all of this requires permits, you should NEVER pull the permits, your contractor(s) need to do this.

Since we have no idea what your contractors are proposing, or if they have covered all the above concerns.
I would have additional receptacles at every new post. Think about where you are going to put your TV, and arrange for cable and power to this location. We had ours installed about 6 feet off the floor so the wires are behind the TV when it is hung on the wall. Make sure you have sufficient drains installed if you plan on occasionally having the windows open, so you have a way to get rid of the water from an occasional passing storm. If you plan on having the area tiled, you may need to have the OLD finish removed so that the new tile will have a suitable surface to be bonded to. The tile should have a crack suppressant barrier installed, the new concrete will crack, and it will move with respect to the original house foundation, if you do not do this you will probably get cracks in your new tile. Get the highest grade windows you can afford, and make sure they have suitable coatings to reduce solar gain. You will need adequate insulation in the original lanai and the new addition.
If I think of anything else, I will add comments later.
Hope this helps, and good luck with your addition.