Mortgage for Multifamily

[Nick Heltemes]

Hello,

I am new to the real estate investment world and have a few questions about obtaining a conventional loan for financing.  I am looking at buying a medium multifamily (30-50 units) and am looking to spend under 1 million.  I've got enough for 20% down, but are banks able to count your monthly income from rent collection for paying your principle and interest?  

Also, I heard from my real estate agent that some sellers could be considered a "second" on a mortgage......I think that's what he called it.  Is this where the seller stays on the note so we can afford a more expensive property.  For example, if we are pre-approved for $900,000 and we find a property that is listed at 1.5 million, can the seller stay on the note and cover the remainder and charge us (the buyer) a monthly percentage?  Does this sound right?

Thanks so much for any advice you can offer.  I really appreciate it.  

Nick