The caterers I share with use the smaller Cadco ovens when they need to take an oven with them for a job; if you are considering opening a baking business and have a commercial space, you would need venting hoods/fans above the oven. The commercial versions are intended to be used and abused in a commercial setting - our convection ovens are on almost the entire day and the heat build up is considerable so the hood fans are on to help with that.
The question about gas versus electric is one of cost (to buy and to operate); if you have gas, then you must have the venting and hoods above the oven in a commercial environment; if you have electric you would need the venting but not necessarily the hoods - if this is for a business, you would need to check with the local board of health for their requirements because every town is different. In a home environment, the building inspector or planning department in your town might be able to tell you what the requirement is.