Just started the research phase and learn everything I can about this process before I make my first purchase. 

What is a good starting place for an estimate to completely overhaul the interior of each 900 sq ft 3br/1ba unit as current tenants move out? 

How much would I have to increase my price point to start finding viable properties in B-class neighborhoods?

Start a new service?

If they put up any sort of resistance, that could be a cue to start digging a little deeper and documenting a bit more thoroughly (hence the doorbell camera coverage tip I put first - installing the cameras right away and then having the new lease conversation with the tenants afterward is very easy to frame as "I'm just a new owner putting some TLC into the property and doing my due diligence on the leases/tenants"; talking to your residents first, finding out they have extra people living there who aren't on the lease, and then installing cameras around the property could set you up for a very adversarial relationship with your inherited tenants). 

Side note, I'm on my way to get my Real Estate License, just passed the exam and starting the interview process with different companies hoping to find the right one .

Quote from @Jason Watson: Michael is right...This is how every comment on this board should start  ;) 

A lot of people with growing portfolios start to look at a true property management software.

So eventually you will have to pay off that note or they will foreclose on you.

Best of luck starting out.