You are mixing up the rules on a HELOC for a personal residential property and any loan for a business use property. The Sch A has a limitation but not the Sch C, Sch E or any other business tax returns.
The only rule you need to follow is the tracing rule where the loan is tied to the business property. SO pay cash and put a lien on the property anytime you wish as all the interest is deductible on the business/rental no matter how it comes about.
