Wait to Get Pre-Approved With FHA?

[Art Maydan]

I'm looking to buy a 2-3 plex in Chicago with FHA and live in it in 6 months. I'm currently only making $30K and living in student housing with my wife (full ride, free housing, sucks but it's free). She graduates in 6 months and is gonna be making ~$50K. Both of our credit is in the high 700s.

Is the amount you get pre-approved for based on your current income? If so, should I wait until she's working so that we have a higher combined income and can get approved for a higher amount? In the meantime, what should I be doing to be successful with this whole house hacking endeavor? Learning more being one obvious answer. 

Also, she starts working in 6 months, but she'll have a contract next month. Is that good enough to get pre-approved or do you need pay stubs?

Thank you!