A platform that will grow (you hope it will get big) should be "hand-coded", on a framework or even from scratch.
Wordpress is for blogs, you can add articles that are SEO friendly. OK! That's it!
After adding or creating a "coupon plugin" you'll see that you'll need more.
As the application is getting bigger, your needs will get bigger.
You'll need reports, maybe an admin panel for your clients, extending your database (maybe creating some partitions) and others.
If you think just to get done the project, my post will not matter.
Just install wordpress.
If it's your project and you care about it, think twice