Oh yes, you're absolutely right, if you meet the requirements for the loan (1/2 time, full time student, I forget, and it may depend on the loan) you can defer your loan(s). If they're subsidized, then your loans won't accrue interest, but if they aren't subsidized, then you'll be accruing interest while in deferment. This can rack up over 5 years or so for a PhD. Of course you can just pay the interest to keep it from capitalizing, or not, and pay for it later. Personally, I've deferred my big federal loan, because half of it is subsidized, but not my higher interest rate private loans. One of them is paid back, and the other is currently in repayment. It makes sense financially to defer your lowest interest rate loans if you can, and divert those funds to paying off your highest interest rate loans first.
At my University, the grad students can purchase the University health plan. The cost isn't included, (around $1000 for a year) but it is subsidized, so we'll get reimbursed for half of the price. Coming up soon already. Plus the University has a good health center which is free for students. The health insurance is good for extra costs that aren't covered by the health center, prescriptions and so forth.
Congratulations on making it as a single mom, I don't pretend to know what that is like, but it can't be easy. FWIW, the first paragraph in my health care brochure fine print says that it doesn't cover spouses or children.
I agree, getting a check and taking classes at the same time is a very nice arrangement. Reinforces the choice of quitting a job for grad school.