If I purchase a 1.4M property owner finance, how long after closing may I refinance with a hud loan

You can refinance at any point after the closing. There is no seasoning issues. Yet remember Jumbo loans are tuff to get these days are require a sizeable down payment. 7% is not to bad of a rate,, its the balloon I would be scared of. Try to extend the ballon period out to at least 3 years if you can. If you have any other questions feel free to contact me at 720-434-6010

It all depends on the terms established with the seller. Although not common, there can be prepayment penalties.
What can of HUD loan are you going to get on an investment property? I'm interested because I was unaware of HUD financing for investment acquisition.