Investment Info:

Single-family residence buy & hold investment.

Was purchased as our primary residence, then we moved and have been renting it out.

Many years prior to her passing she moved out of the home to live with another family and the home sat vacant for a very long time without anyone checking on it.

As long as you Have the income to pay for both houses and you have to live in it for one year.

You either need to become an expert and do SEO yourself or hire an agency that has a complete plan and roadmap for getting you to a place where organic motivated leads are flowing to your site at a rate where you are taking down profitable deals each monthMike Plactere of We Buy Long Island Homes Fast is a perfect case study of someone who used this approach and is dominating his market.  

I'm considering short- or long-term rental but current demand is low due to the offseason.

As long as this 4plex would be in a high-cost area then conventional would still be a possibility for you. 

Last month I warned you of the coming heat.

It really depends on what strategy your trying to implement as some areas are better for STR/MTR then long term and vice versa.

My long term goal is to get into Multifamily apartments.

Lastly, renting by the room is a nice mix of increased cash flow and long term appreciation.