So I talked to him yesterday, mainly to see if that would still be a problem.

I am purchasing duplex, just found out after the home inspection it needs a new main water line as the old one is galvanized steel and is affecting the water pressure drastically.

Can ABC LLC continue to be the main contact on behalf of the new Investor?

As a general rule, you want to use an S-corporation.While liability concerns are an issue, that is not the main reason I am saying to use an S-corporation. 

I'm not sure if Indiana offers a non-NFIP insurance option or not but if they are like Ohio than NFIP is your only option... however not all agents understand how NFIP works or how to give you coverage options.If your main goal is checking the box for flood insurance at the lowest possible cost I would suggest asking the bank what is the least amount of coverage  and what is the maximum deductible they will accept - then get an agent to quote it that way.I'm NOT saying this is a good idea to insure your property this way - you really need to investigate the risk and talk with your agent on what your level of risk tolerance is.Many agents will try and quote it at the full reconstruction cost amount like it's an owner occupied property.

It’s a rural river front property and main highway exposure is Airbnb a good option in the valley?

A way that I think I could really come out on top is by living in a garage and renting out the main rooms.

What are the fees, penalties, or other main factors to consider with these accounts?  

One of the main avenues I know that I need to involve myself in is to connect with local Real Estate Agents.

I was thinking one would get licensed in MO and the other in KS for now (mainly because we will both be working for a bit and can cover each other) but not completely sure if we will need to do that so thank you for your honesty.