How big is this code base and how advanced are the features? With only 3 juniors behind the wheel is it really that big? Was it always this small or is this the

How big is this code base and how advanced are the features? With only 3 juniors behind the wheel is it really that big? Was it always this small or is this the leftover maintenance team? Is there documentation, requirements or user stories available for the existing features? Is it B2B or B2C? If it's B2B it becomes a lot easier to do customer survey of what is actually used and could help you remove half of the 12 year legacy. Apart from the lack of source control, the rest of the issues, while being far from best practices, honestly don't sound extremely bad. Lack of framework or DI is not an antipattern in itself, even if it of course can be. Productivity of 3 juniors, split across one stack each, doing both operations and feature development on such a big application is going to be small even if using better practices. If revenue really is 20M and this code is critical, it sounds like you are understaffed. Skipping the scm, deployment and process improvements, as others already gave good suggestions. Assuming you need to keep the existing code. One thing that has not been mentioned in static analysis. If the majority of the rats nest is in PHP, one thing you should do to add static type checking. This has zero effect on production and makes the code infinitely easier to navigate. This will expose how much of the code that is dead, how much is shared, what depends on what, etc. From here, refactoring will be a lot easier and safer. As others suggested you obviously need tests around it as well.