I think some of your questions have been answered on this thread already. But here are some quick facts for you.
To drive a newly purchased vehicle home, all you need is the bill of sale and title and insurance and you can drive a vehicle that day, temporarily.
If you are going to continue driving the vehicle after that day, you will need to get temporary tags. To do so, you will need the VIN number and proof of insurance. Present those two items at the DMV for your county of residence, and you will be able to get temporary tags for the bus.
If the bus has a gross vehicle weight rating of over 26 thousand pounds, you will need a CDL to drive legally, no matter if it has the seats or not, until you have successfully converted the bus to a motor home and had it retitled as such.
You will only need an emissions test if you are registering the bus in a county that required them.
You will also need a VIN inspection if the bus was purchased out of state, or if you are attempting to alter the designation on the title of the bus from bus to Motorhome.
If you are altering the designation on the title of the bus from bus to motor home, you will also need a weight slip from a certified scale, like the kind you would find at a truck stop.
A lot of people, myself included, do not worry about having a CDL for the purposes of driving a bus home and just pray to the good Lord above that things will work out alright. Generally they do
At all times, it is strongly advised to have insurance coverage of some sort.
If you can call the clerk and recorders office or DMV office in your county of residence It's what we pay our tax money for