What you need?
Trust. People have to trust you/your company to deposit money / coins there.
Safety. You have to make sure people's money / coins are safe. Cold storage, insurance are things to think of.
Usability. Your exchange's usability has to be very good.
Coins. You have to get many coins, but each coin means wallet(s) eating up resources.
Fees. Your fees (exchange and withdrawal too) may have to be lower than the competition at least for the start, until you gain liquidity.
Liquidity. You have to invest and attract people with coins. If nobody has anything to sell/buy on the exchange, there's no reason to go there.
Quite a lot of work and money there. Much more than "having bought a script".
Hopefully people will come to trust the exchange with time and positive feedback from the first time users, I'm implementing a feedback system where people can give feedback on each trader and they can know the reliable and trusted traders. I don't have any coins I just hope people are willing to trade there. My fees will definitely be lower than other exchanges.
Is this the best place to find people who can test the exchange? And what is the best way to convince people with coins to trade there? I know it will take a lot of work and I am willing to do the work.