Are you imagining the arch as filling the middle panel, and the smaller two side pieces as not having the arch in at all?
1. It is trivially easy to cut up the current image like that, anyone could do it in two minutes.
1A. You are looking up at quite an angle. Would you like a small degree of perspective adjustment, I think that might improve the look. One minute.
2. What would be a more interesting challenge would be making the picture as if you had taken it a bit wider, so the side panels are not so small. I estimate 10-15 minutes to do that.
3. The final stages of adding artwork, framing etc are very personal, it would be better if you did that yourself.
If you like I'll give steps 1, 1A and 2 a go if you email me the nef, I assume you want it processed to look like the image above? Free of course. I'll send you a message with my email in case you would like me to do it - I would post a small version of what I do here so people can see, and send you the three full quality images.
PS. I'm assuming you are wanting to print. You will need to specify the following technical information to the person doing the post processing, this depends on who is printing it and how. Even if you are not printing, now is the time to decide what you want.
1. File format: JPG, 8 bit TIFF, 16 bit TIFF, 8 bit PSD, 16 bit PSD.
2. Colour profile: sRGB, aRGB, ProPhoto.
If you are using a (genuine) professional print service you need to ask them exactly what they expect from you. You will also need to choose the paper.
If you are using a normal print service just go for JPG (very high quality) and sRGB. And that's what you need anyway to show photos on the internet.
