For instance, if there was a total of $250K of debt on those properties that woud leave you with $350K of proceeds to use to purchase $600K of real estate.  

Owning a duplex at 20 is a huge accomplishment, and it’s inspiring to see you’re already planning your next move.From my perspective, real estate investing is a long-term game focused on building equity, paying down debt, and maintaining stability over chasing short-term cash flow.

Trying to decide if we should use a home equity loan for the remodel, do we need to put current home under LLC to help with debt to income ratio & would that affect getting the home equity loan?

Most lenders I've worked with will use the lesser of the current rents or market rents reported by the appraiser when calculating your debt service coverage ratio. 

I really like Lease to own option to get into deals without having to take on massive debt.

Any repair issues the new acquisition has you will feel to much greater magnitude due to the property carrying a lot of debt.

Does not affect your debt to income for future loans in the mortgage industry (auto loans could look different, but i would think similar so hopefully no worries there). 

While I do maintain a relatively modest percentage of my assets in money market instruments, corporate debt funds, and high dividend stocks, I remain most comfortable with the investments I specialize in and know best.  

While I doubt I'll be investing here (terrified that property taxes and the pension debt will ultimately cripple property values), I'm always interested in meeting new people.

You want this to be your backup plan if things take longer than anticipated, you do not want to dip into personal credit cards so i would use a heloc to help with down payment but try to keep a nice available balance on a heloc as your insurance policy.