I never foiled on any support and went directly into the waves, so it can be done, but a boat session will help get quickly with the lateral balance, and practicing stopping the initial lift.
Note that choosing the proper wave conditions is essential for a quick foil progression: you must seek gently "walling" swells, ideally breaking only at the top: the less the wave changes shape, the better. Avoid waves with a defined peak and shoulder. A light onshore wind helps a lot.
You can read the log of my boat-less progress at
www.seabreeze.com.au/forums/Stand-Up-Paddle/Foiling/SUP-foiling--my-first-steps-I would advise boat sessions if you do not have waves often, to avoid frustration with "wasting" SUP sessions, or if you have easy access to a boat. Otherwise, no need to desperately seek boat sessions.