All input and advice appreciated

[Gabriel Stabile]

My wife and I recently relocated to North Carolina and we have an opportunity to put an offer in on our first home. 

FINANCIALS: 

Wife has been a teacher for last 3 years and already signed a new contract with her new school down here, she is salaried for $35,000 ($2900/month) and she has $0 debt. Has one credit card that is paid off monthly, $0 in student loans or any other installments. 

I am working for a start up company, am contracted to receive salary ($2700/month) for first 9 months while then moving to commission only. Plus, I have a hefty student loan payment, as well as a car payment. 

From everything I can tell, I think it would be beneficial to put the mortgage solely in her name. 

We also have $20,000 towards a down payment but would like to use as little as of that as possible as this home could use some updating. 

THE POTENTIAL HOUSE:

3 bed/2 bath about 1500 sq. feet on a 1/2 acre lot about 6 miles from beach access. ALSO ON THE PROPERTY, is a detached 2 car garage with full shower in the garage. Above the garage is a tenant occupied 1 bed 1 bath apartment (about 600 sq feet) with laundry in unit as well as a full bath. He pays $600 a month plus utilities and has a lease in place for another year with no plans to leave for the foreseeable future. 

They are opening the listing at $256,000 which is out of the budget we have planned, but as far as I am calculating, we would be looking at a mortgage payment of around $1600 (based on a 4.5% interest rate). 

The questions I have are the following:

Can we use the rent from the tenant towards our monthly income since he has a lease in place? Would it only be 75% of the $600 a month? I feel like I am receiving conflicting answers.

Secondly, we are obviously new to North Carolina, are there any first time home buyer grants? My wife graduated with her masters within the last 2 years, are there any new grad grants she would qualify for?

Any and all input would be great. If anyone thinks this is a good/bad idea, what other things we should be considering that we may not be, etc. Thank you BP community, you guys rock.