Overall a very good conversation, with valid points on both sides.

If you're doing it all cash, you could conceivable do it within 15 days if there aren't any issues.If you don't have an accepted offer in writing, like with an offer binder or a sales contract, your offer isn't valid.

Can I create a new lease with the new tenant while current lease is still valid ?

Due diligence costs are sort of like buying gas to get to work, just an ongoing nonreimbursed expense.

Evaluate comparable rentals to validate market rent, crime stats to ensure the area is decent.

I also tested their social security number verification by using a number that I know does not match the name, and it came back as "validated"! 

Plus a hard money lender usually helps validate if this is a good deal or not, it's always nice to get some validation you're making a good business decision.

The "leverage as much as you can" ideology rubs a lot of people the wrong way, but there's some validity behind that fear. 

Of course, if it turns out it's a great  rental and you don't need the cash, just hold it as a rental even longer, skip the 121 exemption and use the 1031 whenever you're ready to sell.If it sounds complicated, it sort of is, and you must have a Qualified Intermediary on your team prior to selling your property in order for the 1031 to be valid, so the first step would be finding a trustworthy CPA and QI to make sure all your tax docs are in order.

I believe it does validate to certain guests that I am serious about what I do and I have referred repeat guests & friends to the site, but really nothing more than that so far.