I turn the autofocus OFF at macro working distance (0.25x to 1x and beyond). Some people like to use their 100, 105, 150, 180mm macro lens as a portrait lens as well. If you don't plan this use, you don't need AF. What subject do you wish to shoot? Insects need longer focal length (more working distance) because they may get skittish. Bug shooters go for 150, 180, 200mm macro lenses. Dragonfly and butterfly shooters like the Canon 300mm f/4 which has native maximum magnification of 0.3, enough to get the entire insect to fill the frame. Flowers don't care how close the front element gets. A 50, 60, 65, 70mm lens is fine for flowers.
Do you have a decent recent vintage Canon body? Maybe you shouldn't switch, unless you want the D800/E for landscape or other uses. Canon makes the one and only 1X to 5X macro lens in production, the MP-E 65. The lens is manual focus and does not focus in the non-macro range (no infinity). This replaces the need for bellows or stacked extension tubes for greater than 1:1 photos. Check out any macro forum and you will see photos from the MP-E, or go to myrmecos.net for examples of ant photography. Canon really has excellent macro glass. I use the EF-S 60mm f/2.8, EF 180mm L f/3.5, and the MP-E 65 65mm f/2.8, none of which have image stabilization. One of the top-selling Canon lenses is the 100mm f/2.8 L macro with image stabilization - popular because the lens functions well as an ordinary non-macro medium telephoto as well as macro, and because the image stabilization is useful in the not-quite-macro range.
Nikon had a unique tilt-swing bellows that can be chased down on ebay (if you are lucky): PB4. I am not a Nikon user, so I can't comment with authority. This would be the way to get greater than 1:1 reproduction if you have a Nikon. Novoflex may have a similar TS bellows. Lens for bellows can be a reversed normal (50mm-ish) lens with manual aperture - 100 bucks of lens plus under 10 bucks for adapter.
If you are a novice macro shooter, stay with the 0.3X to 1X range before trying for greater than 1X. Also, put a decent amount of thought into your lighting setup. For lighting ideas, see the Fred Miranda macro forum top thread "Show your set-up" - dozens of store-bought and home-made lighting modifications.