I was under contact on a property and was 2 weeks away from close, so I was going to lose the deal and my deposit.

Require a non-refundable security deposit to hold it for them. 

@Keith Todd I also think investors are a fine way to start-that's likely because my personality matches most of theirs.

I was thinking if I can't do s sub 2 I can do what Bill suggested and Lease option it to a tennant buyer, collect 5k as a deposit and pay what it owed.

We prefer to do move-out walk-throughs with the tenants, so they will not be surprised with how we handle their security deposit.

I need to know if I have any options here other than to risk losing my 3% earnest money deposit and the most amazing house for my family.My wife and I made an offer on a bigger house and we were very fortunate that the buyer picked us.  

They can set you up on automatic for anything that matches what you're trying to comp.  

When negotiating a contract assignment with your end-buyer, what is the criteria used for determining how much of an earnest deposit to ask for, in order to insure the end-buyer has some skin in the game and is not so prone ti back out of the transaction during escrow?

if it is you should extend it around to the other side and again match color with either trim or house color. if it's useless maybe consider taking it down if it won't damage anything. 

Going to the bank to deposit checks is a thing of the past.