I have just gone though it, with my new Work Permit.
While the old WP had address, the new one does not so on the day when I went there to get the appointment they did ask me to obtain a certificate of residence (either ex your Embassy or Immigration).
I got one at Immigration on the same day, took me about 2 hours wait -easy peasy.
Do not forget to ask at DLT the web address and code to perform the Online Training at your home any day before your appointment. Once Training is over (about 1hr with some checks) you will get a QR code, save it and show during the process on the day of appointment.
As per medical certificate, if you will go by Sukhumvit Soi 99 DLT, I do recommend to get one on the same day of the appointment at the small clinic located opposite side of Sukhumvit 50mt north from BTS exit. Fast and cheap (I think 140-150 THB or so, 5min wait).
Note there are three counters in the DLT office for the booking and the start of process, one of them is for Foreigner, queue there.