They must be able to demonstrate that they can afford to carry the lease payment and have the economic ability at the end to complete the purchase and sale.

You're brave and valuable to others for sharing these mistakes, and it is this sort of forthcoming-ness that demonstrates you're capable of cutting to the chase, so I am sure you'll take some of the great advice above.  

If not, is there another document that I should request be used to demonstrate our relationship?

If the house is in the right zip code, on a quiet street, I go see the house and talk to the sellers.And I first act like a buyer, not a LEASE OPTION SEMINAR GRADUATE.I demonstrate all the seller's options IN PERSON.1.

There is no statutory holding period but the length of time that you have held the property can go a long way to demonstrating your intent.  

Document what in the conversation and actions demonstrate that they might not be a good fit to avoid age discrimination charges.#2 for how long?

Joshua Dorkin and Brandon Turner's primer on REI has really piqued my interest and has demonstrated that investing in real estate isn't as daunting as I always feared.  

I submit that @Steve Vaughan is absolutely correct this is a very very dangerous play for the average person who has not demonstrated any ability to save money.. you just bury yourself in debt and if your deals don't go well... ( See many storied of first timers losing money) now your really Fubared ... you lost money and you have a mountain of CC debt which will absolutely hammer your once pristine FICO.Now if you have an AMEX black card with no limit or Very high limit say 200 to 500k well then go for it.

YOU would need precedent demonstrating THEM to be wrong, not the other way around.

Long story.I share that to demonstrate how badly funds were managed.