the hotel register you with immigration and print out proof of address is off immigration then has to be shown in immigration office, they will give you official tm30 card stapled in your passport for extension
yes, pretty straight forward, they'll direct you to where you need to be in each stage, had to call back next day to pick passport up, I booked into a hotel to get proof of address they told me immigration registration page won't let them enter details for print out of less than 5 days, I did experience same thing previously in bkk