I'm leaning towards separate bank accounts to be safe.

You should call a couple local banks to discuss the types of investments you may be looking for.Alternatively, a great strategy for someone just starting out is House Hacking.

It is very tough to go from a SFH single family to a 2-4 unit as it does not make much sense to the bank or underwriter.

SOS......I closed on my investment property last Thursday, lawyer, title co, realtors paid and keys handed over to buyer but the wire from the bank ( the title company uses) keeps getting rejected by my investment company.  

Bank would not do HELOC for me because I already have their maximum number of mortgages.

It's a friend or family member and not a business, like a person, they would need to submit a proof of funds from one bank account with a signed letter saying they will provide the funds for the purchase of this address.

I then was offered a position at a local growing investment mortgage bank.

If you are taking about dropping a million cash into properties each year, then yes you are going to want to have some type of reasonable corporate structure, but if you're talking about 25% down 100 grand properties with bank notes, all you really need is some decent insurance.

When the market was slower we even worked directly with the REO bank for the properties and soem of them would do portfolio loans on their own assets. 

I just got off the phone with a law firm doing the foreclosure legal work for a bank.