That engine and transmission are not bad and should be good for 200K+ miles given decent maintenance. It won't be a powerhouse so it won't be climbing hills in the fast lane.
Insurance has been discussed many times on this forum. It is easier to get insurance once the bus is titled as an RV instead of a bus. The challenge is every state has different rules and regulations in regards to titling, registration, and insurance. Your best resource is your personal insurance agent. If you have been getting your insurance online or through a toll-free number you may have problems getting insurance.
Heat loss through the windows can be minimized by a lot of different techniques. The best is removing any windows that are no longer needed. For the windows that are left using insulated curtains/blinds can help.
The tires on that bus are identical to the tires found on 3/4- and 1/ton light duty trucks. Tire prices can go from cheap to expensive depending on brand and ply rating. Figure about $150.00-$300.00 per tire.
The biggest issue with Type 'A' buses like this all have to do with how much they weigh in relation to the GVWR. That particular bus most likely has a GVWR of 12,000 give or take 1,000. Empty weight is going to be around 7,000-8,000. Which gives you at most a net payload of 4,000-5,000. That may sound like a lot but by the time you build in all of your cabinets, plumbing, appliances, and furniture you can eat up 3,000 of that net payload very quickly. Add a passenger or two with all of their junk and plunder and you run out of net payload really fast.