Your best bet would probably be networking with people that are interested in this and competent enough to pull this off correctly(rare). Go trough this plan again and ask yourself how you will be able to compete with established exchanges in terms of security, reliability,fees, UX and volume. It’s not impossible, but it needs good planning and smart decisions to pull off.
Honestly, we don't need another centralized exchange in the first place; after all dozens exist already. It will also be impossible to enter this market anyway; the established giants can easily replicate any 'selling point' a new exchange is going to bring up, and kill it instantly. Be it sidechains, second or third layer support, or lower fees.
There's one thing they can't do: be KYC-less and decentralized. I believe if someone wants to tackle a task as large as creating a whole new CEX, they should seriously consider building a DEX instead, to get more attention, users and competition in this field. Decentralized exchanges are much better for Bitcoin and all of its users, but that's a different topic. Just wanted to get this idea out there.
Regarding the original question: you can't just buy some 'script or source code' and throw together an exchange like that. With the amount of money you'll need for personnel, lawyers, regulatory stuff and server hardware, getting someone to build you the software will be the last / least of your worries. Sort out the rest before; a 'script' alone won't help you much, buddy.
