Does the fold type affect the brochure dimensions I should use?

The fold does not change your flat sheet size, but it absolutely changes your panel dimensions. Two brochures printed on the same 8.5 x 11 sheet will have very different working panels depending on how they fold.

On a tri-fold, make the inner tuck-in panel 1/16 to 1/8 inch narrower so it folds cleanly without buckling.