Too Long; Didn't Read
Sometimes you gotta do what you gotta do to survive in this competitive industry. Any freelancer or developer under pressure knows that it is better to start a new project from scratch.
Working with a project that has an ancient code with a lot of issues is more trouble than it's worth. And, sometimes, the client will not pay for your extra time spent sorting through a legacy mess.
You'll run into default problems, like missing deadlines. Or features that grow into a separated project over time & budget, a client that can't pay for code quality, code that won't be tested appropriately, etc.
It should work, but with a few "small" add-ons that will force you to redo your DB architecture.
We all know how hard it is to support an old code. It's always easier to start from scratch and spend a lot of time while building complex and custom solutions.