Dude not to be a pooper but if you have to come on a forum to ask how to start an exchange you probably ought not to. There are already numerous exchanges run by shadow people who have no idea what they're doing. And that doesn't usually end well.
Haha this.
One of the first things to start and exchange business.
1. Have a dedicated security team
2. Have a marketing team
3. The most important one : A legal team for all potential backlashes and to cover your own asses.
4. A coding team which can be linked to your team 1
If you do not have any knowledge of these 4, especially number 3. You are not meant to open an exchange. Do not try to earn quick bucks and end up getting penetrated by crackers