follow mode will make the camera follow in the yaw axis when moving in either direction on the yaw axis and will stay fixed.
free mode will keep the camera where your cameraman or you left it while adjusting during flight so when moving you have to correct the way of the camera to the object you want to record.
fpv will lock the camera, yes so the pilote is able to see the status of th i1 in horzontal and vertical direction making it easier to fly since the pilot "sits" within the I1 while flying.
Broad answers to that!! Depends on the cameraman and what you are trying to film... I would leave it in FPV if you're a beginner and learn IOC... The free and follow mode are good for Landmark observations, while IOC tends to play a huge role in smoothness... I would suggest FPV for beginners because of multitask confusion! Like I said many answers, depends on the pilot/cameraman... Trial and error..
you got the point. i'd not even start with fpv before not having trained flying. take off, landing, nose in and sideways - this practice is best in the simulator if you have an ipad as stick movements and coordination are good to train there...