Hi.I can easily answer one part of your question. The size of a tank is determined using the equation: Volume = HRT x flow.The volume is for your tank. The HRT is the amount of time the water is in the tank and flow is the amount of water coming from your pump. A HRT can be difficult to assume so try a few differnt times based on what you think. HRT is completely based on the type of process the tank is performing and I do not know any reccomendations for your use.After you have the volume you can use the equation V= 0.7854 x diam. squared x height. This equation will determine tank dimensions. You know V or volume, you should also choose either the diameter or height. You can try many different combinations of tank dimension using this equation. Simply plug a height or dia. into the equation and calculate for the other; Volume will always be the same.As for the pump sizing I would say that only the pump manufacturer or distributor should advise you on this. A pump curve is required and usually held by the pump distributor.In addition you will not be able to determine your tank size until you know the pump outlet flow.