You can switch plans but each time you do, the interest capitalizes. If you are getting forgiveness it will be discharged regardless at 120 payments but it's worth knowing. You can compare and estimate payments for plans here https://studentloanhero.com/ which should give you ballpark figures. Source: almost 2 years ago

When do you finish school? If you have loans with multiple levels of forgiveness, consolidating will bring them all to the highest count. At this point it needs to be done before October. I wouldn't consolidate the Perkins loans because qualify employers can allow you to defer and forgive a percentage annually until they're forgiven over 4 years. I think the only disadvantage is that if you were to pursue an... Source: about 2 years ago

I don’t know if this is helpful but there’s a website that helps you with calculating your course grades, maybe you can use it to double check your maths. Source: about 2 years ago