Structuring Residential/Commercial on 1 property w/ 2 houses

[Jon Frankel]

Hello. I am purchasing a property that consists of a single family house (where I would live) and a three family house (which I would rent out). I plan to take out two mortgages - a smaller residential one for the single family, and larger/higher interest rate for the commercial property.
My question - How to balance the loans? Total property value is $1.9M so if I can value the single family at $500K, $600K or $700K, I think my best bet tax-wise is the smallest value, increasing the value of the three family and therefore the depreciation expense. As well, at some point I plan to knock down the single family and build a two family in it's place, so that keeps the big house basis at a maximum and minimizes cap gains. The difference in combined monthly payments (because of the higher commercial mortgage rates) is negligible.