Yes I train in lease option assignments and  sandwich lease options If you read my posts on BiggerPockets you will learn what you need to know but you still need an attorney  April to September is when you should be working hard to make money 

Is there anyone from New Hampshire that has any sandwich lease experience that would be willing to help me get my feet wet in this niche?

These gurus charge hundreds for teaching Sandwich Lease investing or how to use a real estate calculator.

I understand when doing a sandwich lease option deal, to protect me, i notarize and record the memorandum.

What you've kind of described is called a Sandwich Lease Option. 

Wholesaling, Lease Sandwich Options, and Finders fees are among those that I don't yet know about.

@Carson Scott You could always earn more money for your downpayment by using other real estate investment strategies, such as birddogging, wholesaling or sandwich lease options.

After these documents are signed, I sign with another person, let's call him buyer of this property, "Lease agreement with option to purchase real estate", according to which the buyer undertakes:1) to make me a down payment (non-refundable);2) rents this property for 2 years (maybe 3, it's not important); 3) at the end of this period, gets a mortgage in the Bank and use it to buy this property (refinance) minus down payment; 4) if he couldn't qualify for a mortgage, then he moves out of this property, and the down payment he gave me when we signed the "Lease agreement" remains with me.It seems like a sandwich lease option, but not sure.Thank you for your answers!

@Chaz Martinez  I have more questions than answers.1)  For starters, what type of lease option are you wanting to do:  long term sandwich lease, short term assignment? 

There is always a sandwich lease / lease option if there's a spread between mortgage and rental rates.