Am I able to place the search and view cart components elsewhere on the page, like in the left hand margin?

I am not sure what you are asking?

Will we be able to turn off the right-hand shopping cart in 4.0?

Commerce's Design department can do that for you with custom html. The Search field can be placed in the header too.

Yes, Cwazydawg is correct. 's design team/custom programmers can take care of that in 3.x for you. However, if you can wait another 3-4 weeks 4.0 should be out and allows alot of additional control. Including moving the cart from the right to the left to the top or off all together! 4.0 is gonna rock!