What about arms-length laws?

Sure...but if you sign some sort of arms length transaction paperwork or something else that states in no way will allow the previous owner to rent or buy the property back, you could be facing a nice lawsuit.If you WANT TO ATTEMPT IT, write it right into your purchase contract."

length of time?

If it is in a decent neighborhood a lease option would be a good plan or maybe even a backup plan if you can't sell it within a certain length of time.

If so, your TERM of the loan should be based on how long it will take you to refinance, with Title Seasoning, underwriting lengths, etc.

My accountant says that I can collect the fee from other owners but I am not allowed to collect fees from my own LLC's as that isn't an arms length transaction and it isn't allowed by the IRS.

The length of time is 6 months.

Well, As a wholesaler myself working for a larger company, though the small time guys can sometimes provide property a little cheaper, they can not get better homes, they dont have the relationships, infrastructure, not licensed, insured, bonded, No real backing, and most likely wont be around in the business for any real length of time.

2) What terms would be fair for the loan (interest rate, length of loan, etc.), considering that the 'bank' is my Dad, and I want to give him a good return on his investment.

Those will generally be shorter term rates that do not run the length of the primary term of the lease.