Since I'm going to have to be a landlord, I'm very nervous about what I need to know and what forms I need, etc.

If I were in your shoes and I landed a deal where I would use my 40k as a down payment and cash flow $500-700 monthly you can then use that towards your loans on monthly basis (assuming you keep some for reserves, etc).

I was curious as to whether there is a wait time needed before a landlord could add the monthly rental income he receives from his multi family property onto his own personal income? 

I originally wanted to buy houses and be a landlord but I had no credit history.

Many landlord will install separate utility meters in multis to off load this expense. 

For example, with kicking everyone out in he first 90 days and doing a complete rehab.Joe Fairless says he used Landlords Cashflow Analyzer, www.rentalsoftware.com, but it can't seem to handle that. ($129; Excel-based.) 

Specific to the underlined portion below  "However, tenants who would otherwise have protected status may be evicted if the unit is the only rental unit owned by the landlord in the building"- how would this impact a duplex where the new owner moves into one unit and a protected tenant is in the other unit?

@Ethan Epps- yes, anytime we can divide the land and development cost amongst more for-sale units, we can increase profits.  

Every buyer (whatever that buyer's intention are as a home owner, landlord or whatever) performs his own due diligence and paying property taxes is part of that process.

I have experience appraising high valued homes/land, hotels, storage units, and primarily offices.