To @John Underwood's point, Airdna isn't entirely accurate but they usually come in on the low end so you can always use this as a baseline.Also go with any one of the vacation rental insurance providers he mentioned.
Airbnb charges you 3% if you're a small-time host, or 15% if you're a bigger player. See here for more details.
If you want an easy to know what furnishing could cost, sign up for Furnishr and tell them what you need in your house. That will give you the high end if you buy everything from them and let them install all the furnishings. Another way is to take all of their suggestions and go find secondhand items on craigslist and facebook marketplace to save money. Don't skimp on beds though, because poor bedding ruins the entire experience.
Themes add an extra flair, so if you can afford it go for it. Your goal is to stand out from the competition and themes is one of many ways to do so.
If you have any other questions, feel free to DM me!