I too am deciding on the type of oven to purchase...here's what I know so far.
I've baked in both gas and electic and they work the same. The cakes turned out the same.
In terms of gas/electic bill...right now, the cost of gas is just as high (everywhere). You should contact some local bakeries and try to get an idea from them what their electricity bill looks like. You need to be able to budget for this anyways in your business plan. I've been dealing with restaurant/equipment suppliers and each one will tell you something different gas vs electric. I've almost even been swayed away from using convection ovens, but after using them myself, I find they work wonderfully. If you are in an area where you could possibly rent a commercial kitchen to test drive the ovens, that would be best. In terms of brands you can do some online research and reviews or the equipment. The Blodgett is one that am leaning towards because it is reasonably priced and very well known on the industry. There are a number out there, so I suggest you start doing some research and trials. The last think you want is to have the oven installed and it not work for your cakes.
Also, on another note, because the fan continuously blows in a convection oven cake batter may blow over a bit. For cakes this is solved of course by levelling...for cupcakes, it can be tricky. You need to make sure your recipes will work. They do bake different from household to commercial convection. The more dense the cake, the more stable it will be in the conv. If your batter is quite liquidy/runny, you stand a good chance of batter blowing over the tops of your pans.
Good luck with your selection.