First things first, start using a source code control system from the very first line of code. Get in the habit of checking code in early and often.
Second, decide on a testing strategy. Of course that should mean unit tests, but you should also consider how to automate acceptance tests.
Third, establish a continuous integration server so that your code is built regularly and tested regularly.
Once you have that, as a team establish some simple coding standards. You want your code to be easily readable by everyone. It doesn't really matter what the standards are. Indent with tabs, indent with spaces, curly-brace on the same line, whatever. It doesn't matter what they are, only that everyone consistently applies them.
Since the team is mostly junior developers, plan on reviewing code often to make sure they aren't adding too much technical debt to your system.
Finally, consider using SCRUM. If you do, hire a coach or go to some training. Since you are all doing something you've never done before, establishing realistic deadlines is simply impossible. With SCRUM, your management will have visibility into what you do on a daily basis so they can see what progress is (or isn't) being made. And, since your deadlines were apparently given to you, SCRUM at least guarantees that if you can't meet the deadline, at least you're delivering completed stories on an incremental basis, which arguably is better than coming to the end with a giant system that doesn't work at all.