The question does not provide sufficient information for a precise answer, since impeller diameter, impeller type and rotational speed all have some effect on the power requirement. The mechanical characteristics of the shaft are similarly affected. However, to a first approximation, the power requirement going from 1,000 cp to 10,000 cp, could increase by a factor of 2.5 times. The shaft diameter might have to increase by a factor of 1.5 times.

The answer to both questions depends on the details. A 40-hp motor in a 1,000 cp fluid could be loaded at 5 hp by the impeller and an increase by a factor by even three times would not overload the motor. If the motor is loaded at 35 hp in a 1,000 cp fluid, the motor size, gear reducer size and shaft size may all have to be increased.

The minimum additional information required to answer the two questions are the following: impeller type (pitched-blade, straight-blade, hydrofoil, etc.), number of impellers, impeller diameter(s), number of blades, blade angle, blade width(s), rotational speed, shaft length, current shaft diameter, gear drive size (dimensions and rating). Other dimensional and operating information may be helpful in determining current conditions to estimate new conditions.

The first part of the answer is the safe one. Increase the motor size to 100 hp, increase the shaft size by 50% from the existing size and increase the drive rating accordingly.