First property Seller Financing option

[Michael Smith]

This would be my first purchase I am looking to purchase a 9 unit commercial property with 90% Occupancy. Has a NOI of $35,000 yr. I am running a blank how to structure the deal. The seller is selling for $300,000. He wants $100k and is willing to hold a note on 200k for 5 years. My end goal is to obtain the property refinance both notes commercially with 60,000 down when able to. I did find a hard money lender willing to loan me the $100k down as a 2nd position lean at 20% with me bringing 20,000 to the table. I am pretty sure the seller has a mortgage for $175,000. How am I able to protect the 2nd Lien/investment? How should I structure this with the mortgage it could cause a due on sale clause. I really want the property and this would be profitable. The numbers will work. With it being my first investment I would occupy handle property management on site. What buying Strategy/financing should I use to get this deal to happen. Again drawing a blank with the mortgage and the seller wanting a $100,000 upfront. Please any Insight and help would be much appreciated.