I just created a carrot investor site and am in the process of creating my social media presence.

This can be done via podcasting, blogging, videos, on any social media.

What are other tax implications and challenges I should be aware of if I were to do this?

Build up her social media and web presence and work on lead generation tactics. 

It is really a conversation you should have with an attorney (who can draft the documents) and a CPA who can explain to you gift tax implications, Trust tax administration, etc.

I'm going to start investing in multifamily in the united states but everyone I've talked to so far says financing will be difficult as I don't have a US social insurance number or credit history.

-Add in links to your social media profile(s).

They had monthly meetings for the past 10 years, not sure they still do with the social distancing thing but once this blows over that would be a great way for you to connect with other local investors.

Asset protection, legal implications and business organization are paramount the larger you go.

Third, if you end not renting it out before the current tenant moves out, consider setting up a standard process for screening out tire-kickers and handling scheduling and viewing of the space remotely (if possible) out of respect for social distancing needs or at least with an eye to minimize contact with applicants (to protect both you/your PM and them).