My current plan for my first investment is to find a great deal on a two or three flat, then purchase it with a FHA or 203K loan for the smaller down payment and live in one of the units.

I have an open apartment and showed it to a group of three friends.  

If there are one or two small credit issues such as being thirty days late and it occurred three or more years ago, that is fine.

Seller financing usually comes into play because of three situations1- Property is not financable (construction defect, hazard, uninsurable, needs extensive rehab, etc.)                                                  

So you can do one of three things:(1) prepare a mock 1040 as you normally would as this will give you a high level of accuracy if prepared correctly;(2) review your previous returns and determine your effective tax rate, then apply that rate to this years earnings; (3) have a CPA do it.I get this request all the time so I've built a template for myself that allows me to quickly estimate a client's tax liability.

lead generation, insurance, license, MLS subscription, EKey (allows you to get into houses)subscription.

All three are at risk for ID theft, but you can't get the CR without them. 

Im also in NY and have been investing in Ocala for almost three years now.

Your below 300k budget will get you a nice home in all three areas. 

Two or three cash-out refis from now, it'll get too convoluted to do that.