In planning to sell the final bed and breakfast 5 years ago I bought a duplex.

If you wanted to work with a developer/builder, I would think with our engineering backgroud, you should be able to be a project manager, forward planning, even acquistions associate, albeit with some training. 

I buy the 5 year warranty on all my appliances now and Lowes told me that if I keep the receipt and don’t use the warranty after 5 years I can call and get a partial refund on the price.

If you bank at a retail bank it's likely that you could pull a cashier's check to provide  certified funds.As to the wisdom of using other people's money (that you are solely responsible for) you'd better be comfortable with repayment even if things don't work out as planned.

•I plan to put 20% down on this new property, which means I’ll be left with about $80,000 in cash after the purchase.Given this scenario, I’m trying to decide whether to pay cash for the second property or continue with the 20% down strategy .

If you ever plan to develop the land and sell it you'll use a title company and they'll do the research then, and if there is an issue in the chain of title then you'll wish you did it on the front end.  

If you are going to engage an architect and do full plans and permits, then you will likely need to do some pretty serious analysis.

My plan would be to live in it for a year and then start renting it out. 

If you plan to invest somewhere else, who is the top agent for investments in the area that could point you to a good mentor, or offer mentorship themselves?

Plan for your next property but there's no reason to rush into something so quickly.