It looks like you have received a lot of good answers to your question. I would agree with get a Realtor to represent you and they will recomend several lenders for you to speak with, rule of thumb is going to be 3.5% down minimum.
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However, with my experience with buyers, you could have a down payment of 0% to 20% depending on the type of loan, your credit score, income, location of the property, and the type of property you are purchasing. In addition to the down payment, the buyer has closing cost (expenses) in purchasing a home.
The process sounds difficult but it isn't. A good lender and REALTOR can guide you through the process with ease. It is worth it!!
Well, much depends on whether the complex is approved for certain types of loans and what sort of financing is acceptable to the seller. However, here are some scenarios 1) FHA loan you will need to put down 3.5% but the complex must be FHA approved and the seller willing to accept this type of financing 2) If you're a veteran, you can get a VA loan with zero down 3) Conventional financing of 20% down 4) Lastly, there are many types of loan programs with as little down as 5%,10% or 15%.
I would suggest contacting a lender in your area and discussing all the various loan options with them to find out which one would work best for you.
Good luck with your house hunting!