I definitely would want the mail to go to the correct place.If someone wanted to sue you, the fact that you ignored changing your address would be a good argument that you are not maintaining corporate formalities, potentially having the protections of your LLC ignored.Most states have annual filing requirements for the LLCs so that would be a good time to update it.  

., "I will buy at least one single-family home, duplex, triplex, or fourplex before the end of 2019") and then do it.

One thing to consider is also looking at other homes on zillow around your address, if you see that everyone is doing homes the same way then yes, you should consider what color, tile, and updates can really make yours standout. 

I did a HELOC on my primary property to buy this one, which I rent and the cash flow is good.

@Elani Sevilla, just because you do not have a W2 job, does not mean that you will have a hard time qualifying for a loan.

One of the few multi family properties in this SF neighborhood that had gone up for sale in the last 3 years. 3 story on a large lot, 1952 build with great bones.

I am thinking about buying a duplex, fixing it up, living in one unit while renting out the other.

Most people hire  an attorney to (a) save time; (b) trouble spot issues.

The goal is to accumulate investment properties over time—either fractionally or entirely—bringing them all together under this LLC. 

I have seen fractional shares of some real estate funds on a specific propery - but personally I would want to invest in every property in the fund not a specific one.