What size RV do you have now? Have you done some long trips with it? If so, are you comfortable with the space?
Full-timers live in all sizes - even the little Scamp trailers or a truck camper. It just depends on YOU - no one else. Keep in mind your need for storage space and what you're going to take with you. Mentally decide where you're going to store it and if the motorhome has the storage capacity. Also, the more slides you have the less storage you'll have. Do you need a dance floor or the storage space?
Best of luck in your new lifestyle!