Accountant – Preferably a CPA. 

Where I am running into an issue is there is a delinquent account on my credit history.

Beyond real estate investing, BiggerPockets Money has great episodes on how to avoid the middle class trap with your investments - ie how to structure your investment best so that they're not all locked up in accounts with penalties until you're 65. 

I have a large lump sum saved in an investment account for down-payment and any additional costs.

That is the basic run down, I would suggest syncing up with a real estate knowledge accountant for your specific situation! 

However, I got caught up during creating my listing because it looked like I needed to have another account (Stripe?

It would be far simpler to put the $500,000 in a bank account owned by the LLC and you immediately own a fixed percent.

We also have a bank account at a smaller Chicago community bank, but there technology isn't as good to be honest.I think @Jonathan Greene's main point is don't step over dollars to pick up pennies. 

Provide a detailed accounting of deductions, along with the invoices, to show you’re acting in good faith.

Biggerpockets has a ton of free accountability groups which will keep you on track for your first investment and also teach you along the way!