I'm not a huge parade person, but I would give at least 2 hours minimum to get to your desired spot for parade viewing. This would be assuming you got all your rides/attractions scripted. On your way to wherever your spot may be, definitely get some snacks to munch on to quell your young buckaroos' hunger.
When I tried to scope a spot in a similar manner for fireworks in the Magic Kingdom, many spots were taken by the time I finished Tron.
In respect to the Uber, yes the rates are fluid and can change unexpectedly. Be prepared to shell out Disney gift shop level prices getting back to wherever your hotel may be. You'll also need to be patient as well, as waits also vary. If you're leaving before fireworks (weather allowing) and in your case after the parade, you shouldn't be waiting too long. If it's after the fireworks and near closing, you'll be waiting a long time at the rideshare area while the Disney Transport buses whoosh by.