What is a fair way to split profits on this transaction?

Even if I have him sign escrow instructions and his grant deed and deliver back to escrow, he can still instruct escrow not to record if he decided to.This property is around 600k, so my monthly carrying costs will be around 5k/mo. 

Online payments are paperless and hassle-free if you can get your tenants sign up for it. 

But if it's in your lease & both parties sign it, is it enforceable?

He said as long as I put up a sign, it rents very quickly.

one basic reason is because if you ever needed to get that property back in your name or move it into a trust, etc, the transaction of removing it from the s Corp would be considered a sale and the s Corp would be liable for taxes from the gain, even though you’re moving it from an entity you own to yourself.

As far as penalties for taking more time , The contract I would have you sign doesnt have anything close to that in it .

Since you're doing this on your own, you'll need to get a sales contract with the offer terms and have the seller sign it.

You can test how confident she really is in her friend’s ability to pay by asking if she’d be willing to co-sign for him, just to gauge her response.

If so, if he and I sign on a paper, is that sufficient ?