Platforms like AirDNA and STRata.com provide data on rental income, occupancy rates, and competition in specific areas.

You don't have multiple income streams like you would with multi-family The key is having the right local teams in place.

3) since we will use a local property mgmt firm for marketing / bookings / rent collection, What business is the LLc in and what income and expenses do you report as those of the LLC (vs what do you maintain personally)?

Purchasing your primary with this money, unless it produces income, will likely cost more at the higher interest rates of today vs what you have as a rate on this property.

I've applied for a conventional loan: 3 units, owner occupied, NJ, 5% down.I have enough W2 income to cover the loan and additionally, there are two units rented already. 

We plan to convert the sale proceeds into multiple properties to create passive income. 

On my long time STR, occupancy (70%) and income is down.  

After that they would own a passive 40% of a rental that would pay them a tax free gain every few years.  

Also maybe turning it into a two family home to maximize rental income is an idea.  

Syndication a good way for an unexperienced and or passive investor to invest captital in RE, but not a way to scale.