@Rhona0 , please try not to get nervous now! I know, one can get the jitters once you read some of the horror stories here, but you got lovely reviews, people love your studio - and you made superhost - so you're totally on the right track!
As far as insurance, tax situation, etc, that is up to us hosts to organize and to take care of, as any business owner would have to. most anything you'd want to know about relating to Airbnb is covered in the Airbnb help section online. Yes, their phone numbers are hard to find, dig a bit, also use the search function here, and you'll find a number for Canada in no time.
I see that you have been very successful with your studio, but that renting out the whole house is new for you. If i may, let me just bring up a few points that could possible cause some problems, you might want to define your listing and rules a bit:
1. the more people you allow in, the more potential trouble..... you suggested that even 10 people could stay there, that is a lot!! Have you thought about renting the two different levels/ units seperately, limitig each to 4 people and charging just as much for each unit as you do now for the whole house? I bet you'd get even more rental requests that way - and more peace of mind!
2. I would be more specific in what exactly comes with the rental space, it isn't clear to me looking it over, as you also have pics of the studio in your pics of the house. I would not put explanations of the space/ house into your personal profile, but all in the proper sections of the rentals. In case you make 2 units out of the place, be very clear and consistent in the photos and description. Right now I see your rental bikes as $25 in your profile, $20 in the house description, and $15 in the studio write up. Which one is it?
3. the more you rent out, the more you also need to make sure you won't get worn out. You might want to consider changing you cancellation settings from flexible to moderate, to have specified check in times, to perhaps remove the trampoline and massage table from the studio . if you have kids coming, that could spell trouble. I also find the long term rental potentially troublesome, especially with the "wrong" people. At my place, I limit stays to 2-4 days. Nothing wrong with having specifics in your house rules.
And now, keep on doing what you're already doing so well - good luck!
AnnetteP
Ps: I don't understand what you mean with people claiming their vacation costs and Airbnb not backing you.