1. The maximum overdraft limit is not necessarily your overdraft. So double check  what your actual limit is once you have opened the account.
2. If you don't have access to the maximum possible overdraft then the best idea is to have monies deposited in the account regularly. Even moving money through the account on a regular basis will aid your getting a larger overdraft.
3. If you can afford it, and you have an overdraft with a bank that you haven't made full use of, take the full overdraft amount and put it in a savings account ... and then do not touch the account until you are depositing.

If your intent is to make money out of these large overdrafts, then you should take the Halifax student account. If the overdraft is less than £3000 intially, try and have loans payments or other deposits put through this account first. After the deposits are in the account you can take them out and put them in an easy access savings account, or an express account. Take the overdraft amount out, and put this in a savings account also. While interest rates are not good for savers at the moment, one can still get a easy access savings account with 5% from ING.