You want to lift something up but not pay someone else to do it first. 

Tenant will pay for installation costs and provide receipts as evidence;2.

In my state that would be an expensive change as I would be paying state transfer tax on the move along with other costs plus I would need to consider whether I wanted to buy title insurance on the property for the new LLC.

Depending on how you are planning to pay your friend  the profit out of the transaction.

IfIf you do not know what you're doing with accounting, which most people don't, I would recommend that you simply bite the bullet and pay someone to handle it.

He has also mentioned that his job has been paying him late here and there.

I pay around 2400 as rent and I've calculated my monthly expenses will be around 3700 if I buy a condo. 

Should I pay her more $ for longer stays like this or just pay her the same fee? 

I’m thinking of taking my friend up on a 25% interest promissory note for his company just so I can cover the $2k/month interest I’m paying on this equity cash out.

It's going to be nearly impossible to ballpark based on what others might be paying.