"Also, the higher you raise the enlarger head, the longer the printing exposure times"--Not true. At the same aperture, with the same negative, but different lenses (setting aside the issue of differences in light transmission due to the properties of the glass and coatings), the exposure time depends only on the degree of magnification. If you make a 5x enlargement from a 35mm neg with a 50mm lens at f:8, the exposure will be the same as a 5x enlargement with any other lens at f:8, because you are spreading the same amount of light over the same area on the baseboard.
"and the enlarger then becomes prone to vibration. "--This is true and worth considering.