First of all you need to prepare a Proof of concept (POC) by taking care of below aspects:
1. Discuss with development team and get access to bugs reports.
2. Do a simple pareto analysis by seggregating the defects into different categories (Requirements defects, Design defects, coding defects, environment defects).
3. With the above analysis, you can clearly showcase that maximum defects are with coding faults only and can be caught by testing team before going for production deployment.
4. Prepare a test plan (Requirements undestanding, Test case design, Select a open source test management tool like TestLink, bug tracking tool like bugzilla or Jira, Test strategy)
5. Start the testing by taking one module and perform both test case execution and Exploratory testing.