The 1,500 a room number is in the right neighborhood for a bed, mattress, dresser, desk, chair, and a lamp bought new, and you can do it for 600 to 800 a room buying used, though the used route costs you time and you'll replace pieces sooner. That's only one line though. Here's what else typically shows up.
Each bedroom door needs its own keyed lock, usually 60 to 150 installed depending on whether you use keypad locks. Common areas need furnishing too, sofa, dining table, cookware, and a shared vacuum, and 2,000 to 3,500 is a normal range for a four-bedroom house. Internet has to be good and it's on you, commonly 70 to 110 a month. Most operators pay a cleaner for the kitchen, bathrooms, and living room, and 120 to 200 per visit twice a month is typical. Utilities are usually bundled into the room rent, so budget for whatever the house actually burns rather than a per-tenant estimate.
On software, a small landlord platform that handles four separate leases, four rent payments, and applications generally runs somewhere from free with fees passed to tenants up to roughly 20 to 60 a month for a handful of doors. Prices move, so check current pricing on the site itself.
The cost people underestimate isn't a purchase at all. It's the lease-up. Four rooms don't fill on the same day, and carrying an empty room or two for six to eight weeks while you're paying the full mortgage and the full internet bill is real cash. Set that aside before you spend on the sofa.
One more thing worth confirming early: ask the seller for his room leases and his rental license, if your city requires one, because inheriting four tenants means inheriting whatever he agreed to.