I would upgrade to the bigger tank and when you transport the fish make sure you keep an eye on the temp and keep the fish and shrimp in the water from the tank to ease the stress a bit, also if you keep them covered they will be less stressed from the moving. take your time and plan the move in advance to help avoid complications etc.
I you do decide to change to sand the corys wil love you for as they like to root around in it looking for food, the problem with sand is bubbles of gas can bulid and are toxic to the fish to prevent this you must help oxygenate the sand with stem plants, trumpet snals or use a thin layer of sand. Sand when stirred up wil cloud your tank and wil block the impeller of the filter so when cleaning turn off all the equipment to prevent this. And once you get use to the sand it will be easy to clean and maintain it and the gravel with sand will look more natural provided you use natural colored gravel.