Part time realtor activity with rentals in one LLC?

Tax Strategies
1
Mark, Matt, I recently found your podcast and very happy that I am learning so much! 1. My husband is a part time realtor under Kale Realty. He only use his realtor license to buy rental properties for ourselves. Is it necessary to setup an separate LLC for his realtor activity? We expect he only does 1 or 2 transactions a year, about $6k commission a year, minus about $3k expense. Is it ok to use an existing LLC with rental properties for his realtor activity? What is the difference tax wise, using separate LLC for realtor activity, or using one existing LLC with rental properties?
If we mix passive activity with active activity in one LLC (disregarded), will only the active income pay self employment tax? 2. I did some private lending under my name. One of my friend lent me some money with a promissory note, which I lent out. Can I deduct the interest that I paid my friend as business expense? How to do it? I have some rental under my name too. Can the loss from rental be used to reduce the interest income from private lending? Thank you so much! SunnySusan