You'll have to present a complete picture of the system requirements; for example, you'd need to supply physico-chemical data on the fluid pumped, such as viscosity, density, corrosiveness, chemical stability, lubricity, volatility, toxicity, flammability, amount, size and hardness of suspended particles, possible absorbed gases disengaging within the pump.

State the rpm of your motors, also whether the operation will be continuous or intermittent. You'd have to specify adequate margins to overcome transients, but don't oversize flow rates beyond, say, 20% of design. Consider whether future requirements (already foreseen) could be satisfied with the pump to be selected.
 
For total satisfaction, you'll have to have a full sketch of the circuit, including controls, flow rates, pressures, temperatures, piping sizes, valves and any safety items, spares, etc. It will be of value if at this time you start considering transients and what ifs.


On bid evaluation there will be a plethora of new items to consider and compare
before you reach a decision to purchase.

Have you considered the pressure difference between the two vessels? If pressure of suction vessel is morethan that of discharge vessel, deduct the deference from total head otherwise add it.

25362(I think I should wish you after 19 days) has given valuable suggestions.

Best of Luck.

Taking all the above into account - what material are you using for pipework? how many bends ? Valves etc....have you calculated Friction?

now you have to look at the piping system network connected to your pump. For example, avoid air pockets in your suction piping, consider minimum flow piping and controls for your pump, try to define your range of fluid composions because this will define your minimum and maximum pressure drop across the pump.

Consider mechanical aspects as well as process aspects