You’ve received a lot of great comments here.
Think through your maximum occupancy and make sure ‘it works.’ That is, will guests be comfortable? Maybe you can fit in room for 10-12 to sleep, but if it’s one bathroom and a dining table/seating for four it doesn’t ‘work.’ So set the maximum occupancy appropriately and make sure that your seating and dining match that. [Oops! I see @muddy made this point. Great minds. . .]
Make sure you have two bed pillows per person. So it sounds like 4 x 2 x 2 = 16 pillows.
Get kitchen gear and appliances, like a coffee maker, that are easy to operate and is consistent with what you’re offering, with who you’re seeking to attract.
On towels, folks here have suggested having spare hand towels, wash cloths, bath towels so people who want to change more frequently or use an extra one to dry hair have it available. Most guests won’t ask for more, but have it available, like in a plastic marked bin in a closet.
Make sure your mattresses and all your pillows have protectors from dust mites, bed bugs, stains. I use this brand but I’m sure there are other good ones: Protect-A-Bed AllerZip Smooth Waterproof Pillow Protector, Blocks Bed Bugs, Dust Mites and Allergens, Machine Washable.
Make sure you have an extra duvet cover for each bedroom.
Stay a few might at the STR. Live there for a few days and find what’s missing and what works well. Invite a friend to stay a couple of nights without you. See what they say.
Does the House Manual tell them what they need to know?
Should you label things for the guests who don’t want to read the manual?
Are they comfortable?
Is it super clean?
Is there anything missing that your target market would likely expect?
Is your property safe? Check this out: Is Your Property Safe? Take the Challenge -- A 75-Point Safety Checklist