Thanks for the tip. There's a lot of responsibility involved, especially when dealing with people's funds. Not to mention, I'd need to comply with every single regulation imposed by worldwide governments. Even decentralized exchanges are not exempt from this. The best path to take might be creating a P2P trading platform where people can post their own ads for buying/selling cryptocurrencies in-person. It would be something similar to eBay, where people post their own "item listings" for sale. I believe that with this model, the responsibility would lie on the user himself instead of the owner of the P2P trading platform.
I've seen pre-made scripts available for purchase online, but they look quite risky to me. As you've said earlier, hidden vulnerabilities would expose the exchange towards hacks and theft. In order to create an extremely secure exchange, one needs to hire computer security specialists to maintain the site resistant against online threats. The costs and responsibilities involved in setting a centralized exchange makes it challenging for the newfound entrepreneur. Which is why, my options are limited to either a P2P trading platform, a 0x relayer, or simply an OpenLedger/Bitshares gateway.