Refining the internal portal on PHP, MySL, juery

Our software design company has its own internal employee time portal, written on PHP, MySL, juery. The portal was mainly, unfortunately, developed by Junami, so it does not use some ORM, and the codebase on the one hand is not bad (for example, the data is well normalized everywhere), on the other hand - there are systemic stupid errors of juns.
What is required. At first, in a mode close to 40 hours a week (but it is possible and less, discussed), to correct the most critical bugs, to refine the functionality. Then, for a while, rework the entire codebase to rule out stupid errors. This will take about 20 hours a week.
The project has a project manager, analyst and tester. It is necessary to write code on the above technologies, there are no serious requirements on the front, i.e. the basic knowledge of juery will suffice. There is a test server. Both the test and the os-Linux product, it will need to deploose the project, i.e. basic skills of working with this OS will also be required.
We are looking for a leading developer with a high degree of autonomy. You can offer us your bets, we will evaluate the combination of the level of the developer and the offered rate, preferring the best level for this task.