If you have a well-maintained unit in a decent area, your tenants will want to stay, even if the increase is substantial and it is within market rent.BTW, prior to purchasing, ask the owner for copies of the most recent utility bills, tenant estoppel certificates (signed paper from tenant stating financial terms of the lease) and CLUE report ( A report that lists if any insurance claims have been filed against the property in the last 7 years) to ensure property is insurable.

Would this effect my debt/income ratio?

Spouse may qualify for VA loan, but generally shouldn't have changed his bank loan opportunity, as those are generally filed jointly.Generally PD application, or rather loan qualification based upon PD application is only after you are sworn in, and not any step before it.You will have to prove to the bank that you will have continued income to pay off the debt.

My husband has been reading a lot about financial "freedom" and one topic that got his eye was Real Estate Investing.  

That is what wakes them up and it can cost $500 to $5,000, so thats why its good to have a reserve.Then we attempt to get them repaying or settle for a lump sum and the debt is out of their life, otherwise we foreclose.

I just got financial information and since Jan 2016 the income is up and down several times.

Though I don't know your strategy or your financial situation so that's obviously your call. 

You should base the price on its current financials not pro forma.

I know a few such as financial terms, closing cost, home inspection and appliances.

Without getting into the whole spiel, about a year ago my business partner @Tommy Mejia and I decided that we wanted to become financially independent and decided RE would be the best way for us to reach this goal.