You need a team of people to sit and watch the cold and hot wallets every day, every hour, every minute. You need a team of people to sit and watch the trades as they occur.
If you're all alone or just a small team, like me, for example, you'll never get it big. About the only thing I do on my site (which is not an exchange by the way, but it accepts deposits and withdrawals of BTC), is secure the funds. Since I'm not working on it full time, I make people wait (a bit) if they attempt large withdrawals.
That wait, makes or breaks your business. If it's too long, people don't like it. There is no such thing as "too short" for waiting times, so the shorter the time waiting, or the quicker the support you can give your customers or clients, the better.
The best exchange is the one that accepts your deposits quickly, funds your account, allows you to trade almost instantly, and quickly withdraws either your cryptocoins or your fiat money to your bank accounts. All exchanges aspire to be that.
You will also need a team of people to watch, and that's all they do mostly, watch. For security purposes. They might try to do some penetration testing or whatever or try to crash your exchange on purpose. Or you have some sort of bug bounty for external security.
I would love to run an exchange, or be part of one.
Besides that, you've got to have a support team on stand-by, for inquiries and such.
All-in-all, it's a huge task fit for an organization. That's why it's very interesting to hear or read stories of how exchanges started way back then. Imagine having to deal with all that when the one behind the exchange is just you and your biz partner.
