Yes, sitting down is a good idea especially if you get motion sickness, some people find they get dizzy seeing the landscape flying by while they're standing still. Not that sitting down will make that not happen, but at least you can't fall over if it does...
If possible have a spotter nearby to let you know if you're getting too close to anything that you may not be able to see in the camera field of view and for the first flights it may be easier to be in the middle of the largest unoccupied open space you can find, first flights tend to be very adrenalin producing so make things as easy and relaxing as you can until you start to feel comfortable flying remotely. Took me quite a few flights before I was ready for take off and landings via FPV view, I usually got the multi off the ground, engaged altitude and position hold (Mikrokopter flight controller) then put the goggles on and flew around. Back to landing zone and reverse the procedure to land, goggles off then disengage AH and PH to land visually.
From there I progressed to takeoff and flight but still landing visually and after enough stick time I felt confident to do the entire flight FPV, now I try to land within a small predefined area to see just how accurate I can get on landing, usually within 2 to 3 feet of the takeoff point
Ken
P.S. you may want to do a couple flights without the GoPro in the case until you build some confidence, the case can take a lot of abuse but there's no reason to subject the camera to possible crashing for the first flight or two. Just make sure the center of gravity is correct without the GoPro if you decide to go that route.
