How wide are the spacers?

The spacer are wedges so you can have different widths

Probably not. Remember you have to cover the gap with molding, so measure your molding carefully so that you don't have gaps showing, and shim to that. I've also seen recommendations for 1/4 inch. I doubt that the floor moves that much.

Rule of thumb for me is 1/4" minimum, 1/2" max...have to have room for the installation and also for it to be covered by something 3/4" or slightly smaller (IE:" shoe or 3/4" quarter round)... Remember when putting laminate flooring down you have to have slightly more than 1/4" of space anyway at the ends to tap it back into the tongue and groove ends (The "pulling" tool itself takes up 3/16" of space anyway). So 3/8" is good. as long as there is enough room for the installation and then afterwards, the expansion and contraction that a wood floor will go through almost any size space will work above 1/4"...