AmericaninEurope

No, future income cannot be reported. Even if you start work the day after you apply, you CANNOT claim this income/employment.
It seems like you will have to, by default, apply as unemployed. When I applied I had just stopped teaching in May, moved to another state, and then would begin teaching at another university in August. My income would have placed me well over the poverty line. However, since I could not claim future income, nor past income (technically I was employed by neither school during the summer break), and my husband (the US citizen) was a student with next to no income, we had to get a sponsor.
Could you apply after August 10th an avoid this hassle altogether?

To use the immigrant's income, you need to provide proof that the income will continue from the same source after becoming a permanent resident.

I think it can be tricky to prove support in the form of a graduate assistantship, because, as a grad student your job is only "temporary". If your family can help you through a joint sponsorship I would consider doing that. Me and my husband (he is also a grad student) ended up doing that after talking to some lawyer friends and available lawyers at the university.

You said you just quit your job and are pursuing graduate studies that provides a stipend.
1. What do you mean by "just"? A month ago? Last week? Yesterday?
2. Did you already start graduate school? Are you registered to start in the fall semester?
3. Did you quit and then start school? Or did you work and attend school and subsequently quit the job but not the school?
If you have already started (or started this summer - odd, but possible) and are just on break over the summer, you are not considered unemployed.
If you are starting in the fall and the stipend is future money to be earned, you are considered unemployed.

Hi,
You are not unemployed. You are a graduate student. Your stipend is your compensation for being a graduate student.
List your stipend as income. After all, you do get an income tax form from the school. Many people are unaware that some graduate students have income in the form of a stipend.
If your income does not meet the 125% poverty line, you need 3x the shortfall. It's not 5x. 3x for a spouse. 5x for other immigrants.
You may want to get a Joint Sponsor.
Best of luck.

Assets need to be 5x the poverty line requirement to be used solely.

The form I-130 requires you send just one proof of U.S citizenship. A copy of your biographic page of your U.S passport is sufficient as evidence.