How much can one arduino do?

Hey guys, I am extremely new to this and just needed some clarification. So I am planning on using an arduino to conduct a simple test, measure the load from two different motors via two load cells. Now to make it complicated. I was planning on having a barometric sensor start the motor and to start recording data from the load cell (to save space in the sd card).

Yes you should be able to do all that with a Uno.

Make sure you get the SD card that is compatible with 5V signals.

Assuming you're not going to try and sample the pressures more than tens of thousands of times a second an Uno or equivalent will handle this just fine.