I recall reading an article or blog post about an investor giving their child a wedding gift of pre-paying their first year's mortgage principal.  

Interest only or principal plus interest loan?

As Matthew Brill mentioned, there is a self-sufficiency rule for 3- and 4-unit properties funded with an FHA loan.  85% of the market rents on all four units need to cover your monthly payment (principal, interest, taxes, insurance, and mortgage insurance).

Well I am the principal commercial broker and owner.  

Add that to your $425 principal and interest payment, plus the $75 you budgeted for taxes and insurance, and now your cashflow is negative $25 per month.

Some mortgages require the payer to pay the property tax to the bank, along with the principal and interest payments on the loan. 

The part where I'm not clear on is for an existing rental where tax returns are available.I know that Principal, Interest, and taxes are all included as debt.  

I had a quote of 2.64% for a 4 year term on my principal residence in Canada just today.The US starts around 4% but then you have to add 30 to 40% for the exchange if I use Canadian money for the payments.So, ideally I need to borrow as much as possible for my deals and pay it off as the dollar improves. 

From the mysolo401k website: If a participant wants a repayment period longer than five years, plan administrators should obtain a sworn statement from the participant certifying that the loan is to be used to purchase the participants principal place of residence (a principal residence, has the same meaning as the term under IRC Sec. 121).  

You can also try to find some creative solution to bail yourself out from your current condo faster - I have a friend that rents out all the bedrooms in his place and uses that money to pay down the additional principal.