There's been multiple threads on IBR and such with really in-depth discussion about how it works, it's pros and cons and such, so I would go ahead and do a search to get all the info you need. Google is also very good too
. You can also find loan repayment calculators online that will tell you exactly what your payments will look like based on all the different repayment plans, and how much you'll pay total in your lifetime for each plan.
I'm personally not as worried about IBR being repealed, but I'm very worried about the loan forgiveness programs getting repealed.