Spend some time searching and reading all you can here, all your concerns have been addressed. Check with your state laws for clarification. Most important is to never drive a vehicle on a public road uninsured. Once the bus has been decommissioned it is no longer considered a commercial vehicle if there is not seating for 16 passengers ( not 16 seats). Some states allow driving on the BOS for up to 30 days before registering. Some insurance companies automatically cover you for 7-30 days under your existing auto policy, check with your agent.
Bottom line, don't drive like a jack ass and LEO will have no reason to discuss CDLs. Your bus probably won't go much over the speed limit, so why are you talking to officers? If you get questioned just explain it is a new purchase you are transporting home, here's my BOS, signed over Title, and my proof of insurance. You should be good.
You don't need insurance or registration if it's in your yard under construction and your ot taking it on the open road. You will need a "commercial for private use" policy if you're driving it during construction until it meets the requirements of an RV to qualify for lower RV rates.