I'm 5'4 and sitting on the GV today, I didn't state that I had problems, I mentioned that my feet were not flat on the ground. As already mentioned, I was comfortable but still seemed a little high. Seat was kinda hard so I will have to decide what to do. Based on what I've read in the other threads/posts, with the touring seat I would be even higher so I may consider getting a seat cushion.
Try to ride it first "as is" and see how it works out. Don't be misled by a bit harder seat. Soft is not always the solution, I know that from many motorcycle miles. However, this theme is very "individual", what is OK for me may not be for you and vice versa. But "in general", a bit firmer seat is better for longer distances, a bit softer seat for shorter distances.
Even though putting both feet flat on the ground is comforting, I ride also a quite heavy and high motorcycle (Adventure Tourer) where I chose not to lower it due to loss of cornering capability and off-road ground clearance. There is no problem at a stop; either I have
one foot flat on the ground and the other one on the bike and the bike just a tad tilted over to that side to stabilize all, or, I balance the bike straight-up on my toes, and this is now after years so natural that I never think about it. And we are talking here of an about 1000+ lbs bike with full bags and passengers.
My tip, practice without driving the scooter, tilting left and right, getting the feel of the weight of the scooter;
and, have somebody stand by in case it really wants to fall over! But try to see how the relative weight for you increases when tilted to either side.
General Riding Safety Tip: As an advise for everybody, as I have seen recently so many riders lay their motorcycles and scooters down on gravel/slippery roads, practice on an unpaved/dirt road
braking, first without the front brake, second, with a very moderate use of the front brake, and then front and rear brake together. Gravel, sand, dust can suddenly be there also on paved roads, and if one has no practice, many people usually crash. Remember always for safety: you can lock up the rear wheel on a motorcycle/scooter without any major consequences, but you get instant crash results if the front wheel locks up. So on slippery surfaces the use of the front brake should be very moderate (if at all) and practiced. On dry surfaces the front brake is the most effective one to use for stopping (the rear wheel is not very effective), but on slippery surfaces it is a total different story, and the effective and safe use of front and rear brake depend on many circumstances.
An
advanced Motorcycle Safety Course (one stage higher than the basic course) is a very good investment for everybody, be it a new rider, or also a bit more experienced rider. Because, nobody wants to crash and get injured, and besides that damage your scooter. So, practicing for situations that can happen unexpectedly at any time is a wise safety measure.
Hope this will help to enjoy your GrandVista for a long time.