That's a lot of samples/second - gonna need a fast board like the Due.
Don't ultrasonic sensors use digital signals? You send a ping out, measure the time it takes to pick up an echo - and don't really use the level of the echo.
It only tells you about what is perpindicular to the sensor, otherwise the ping echo goes off in some other direction that the sensor does not see.
Instead of 6 sensors, you could have one mounted on a stepper motor, pan back & forth and combine the known angle of the stepper with distance returned to paint your picture of the surroundings. Could probably stick with the simpler 328P/1284P/2560 series processors for that - I'd go with 1284P for the 16K of SRAM for storing data on the returns.