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 manage each property personally, which has provided me valuable experience but also highlighted the need for a more formal structure as I plan to expand my portfolio.My PlanI'm looking to establish a Wyoming Holding LLC that will be taxed as a partnership.

You will have higher premiums if the property is not operating within a formalized 503c nonprofit entity. 

I just don't have a big market, so it's tough to find something like this particular property as evidence.I was thinking of something more general, like a formal study of various markets, but I haven't found anything except general articles or blogs.

Talk to Real Estate CPA before doing it.I’d recommend putting this $100k in a in an LLC along with rental to formalize the partnership.

A formal agreement would also be smart to avoid any confusion later on.Sounds like you’re in a good spot with the $80k to invest.

It will not be a formal contract or agreement but something where both parties understand the objective. 

You could also reach out to a local, reputable, property management firm to see if they offer a la carte services for lease preparation, application processing, move in inspection, etc, if you are planning to self-manage but need some help with the more formal items.

If so, is this something I can get a template of online or do I need to seek one of these documents from an attorney to then present back to attorney signed by both parties to then draft a formal contract?

Proceed cautiously, judiciously, soberly, and passionately.