I would make one suggestion. Find out the current status of the GSF population. Like most fish, GSF will quickly in an empty pond reproduce so as to fill the pond to carrying capacity. If there are large GSF (4in+) they will have large mouths and eat a lot of offspring and FH and Gams. The biggest risk to your plan is that the pond is already near carrying capacity with GSF. If so it will not support the new fish or the existing GSF. A wild guess here , if you have more than 25 lbs of GSF in the pond now , you should remove as many as possible. If you had BG instead of GSF I would be giving the same advice.