If I were to fix up and furnish my personal residence to rent out as a mid-term rental while away for a few months at a time could I treat these expenses as a business expense? If so, is there a special way to do it and prove it to IRS?

For items like a laptop ($1000-1500) I'm reading that you have to track your usage and you can deduct the amount of usage as a business expense like if you spent 70% of your time on business activities and 30% personal then you can deduct the business portion based on usage. Is this accurate or does that only matter if the item is above a certain dollar threshold?