Hi Edson,
With having just purchased your primary residence (single family) you would be looking at purchasing the multi-unit as an "investment property." Most lenders will require a good explanation if you were to apply for a new primary residence loan within 12 months of purchasing another primary residence. It would also be questioned why you would be moving from a single family to a multi-family property as your primary residence as it is perceived to be a less desirable living situation.
By purchasing the property as an investment property you are looking at a minimum of 25% down for a multi-family, and unfortunately the rates are slightly higher than a primary residence purchase. You can use 75% of the projected rents to help you qualify, but typically the hurdle for most first time investors is the down payment requirements for an investment property.
Please let me know if this makes sense or if you have additional questions. I am a loan originator for a large bank in Boston and can help you with a pre-approval if you are interested.