When can you use the income from one property to buy another?

[Markuz Griffie]

I graduate from law school next year. I am also a 20% disabled service member. I will make 80K, my wife makes about 40k. Used the GI Bill for law school so minimal debt.

I plan to use a VA loan to buy a 4plex (that we could afford on our own anyway) to house-hack. The VA requires that you occupy the property for one year.

After than one year occupancy, at what point can you use the rental income from property A, to satisfy the mortgage on property A, in the eyes of a lender?

If I wanted to use an FHA loan to do the same thing again, will the FHA lender look at the rental income satisfying the original mortgage, or is there a period of time before a FHA lender will include the rental income? I've read that you can include future rental income on an FHA application, but can you include the rental income from the previous place?

I'm new here, doing a lot of research, so if this isn't clear please let me know so I can try to clarify.