First Back-end Project

Hey guys, We are a group of three front end developers who are well versed with most of the front-end aspects. We are planning to get into back-end development next. We just got a project to design a site which has 2 main things,

1) Educational Portal : This has 3 main modules a.Student : Can Search colleges and registered student can ask queries to college b.Colleges: Can set up their profile and add details about their courses c.Admin
: Can manage the colleges / student , edit contents and approve contents etc.

And a

2) Job Portal : This has 3 main modules

a.Student : Can browse, apply for jobs b.Employer: Can post jobs, recruit candidates etc c.Admin : Has to approve jobs and manage student/employer.

Which is the best approach towards building a website like this? We have just a basic understanding of PHP and we aren't sure about how to get started. Couple of forums suggested using Wordpress but we aren't sure about how customisable it is (both back end and front end) and would it be good idea to start coding from scratch using PHP considering the duration of the project i.e 3 months.

We want to build something similar to these

Education portal : www.shiksha.com Job portal : www.naukri.com

We are willing to learn and we just want to know in which direction we should start with, any kind of suggestions or idea would be really appreciated.