Firstly, congratulations on taking the community college to university route. You will save yourself a lot of money, especially in MA, where even state schools are expensive.
1.) Your loans will be in deferment as long as you are a student and are taking enough credits to be enrolled at least half time- this is called in-school deferment. Once you get to UMass, you should go to the Registrar's office and ask if you need to apply for in-school deferment yourself, or if they will be automatically sending your enrollment status to your lender.
2.) There is a lifetime limit to the amount of money you can borrow under the subsidized Stafford loan program. You can check out the FinAid website for more information, but I believe the limit is between $20K-$30K. This amount will not cover the four year cost of your degree (including community college). Are you considering a different loan? Will you be older than 24 when you go to UMass Amherst? In considering your cost at UMass, don’t forget that there are tuition discounts for community college transfer students, as well as a community college transfer student scholarship if you can keep a certain GPA. Look into these.
3.) Where are you considering going to community college? Paying $6K per semester for community college is really expensive. Are you sure this is accurate?
4.) Make sure that you take courses that are transferable to UMass Amherst. There is a program called MassTransfer that ensures that if you take the Mass Transfer block of credits, any public four year institution in MA will have to accept them. Meet with a transfer adviser at your community college to discuss the articulation agreements it has with UMass Amherst.
5.) Visit UMass Amherst yourself and make sure that you like it before you commit to an articulation agreement with that school.