Macro photography is an area where buying your lenses USED makes a lot of sense. Buy from a reputable dealer that has a decent return policy. Many macro lenses are bought, tried out, and then sold back to dealers because the user never really used the darned lens. I've bought all my macro lenses on the used market.
A Sto-Fen diffuser cap works okay, but you get a much larger light source by using something like the Photoflex mini-softboxes. You can position such a mini-softbox on a smart cord, like a Nikon SC-28 TTL Remote cord,either on a bracket like gryponslair is suggesting, or with the help of an assistant, or even held in your left hand. Having a *single* light source aimed at an angle will give some shadows and will help modulate the tones and give shape and dimension to your subjects. There is very little *need* for two-light macro setups, and ringlight lighting was designed for dental and medical and forensic photography, and most real-world macro stuff shot with a ringlight looks dead, dull,and lifeless.
One of the biggest challenges is working distance. With the short lenses like 60 and 70mm, you have a tremendous amount of flash power,and when you change camera-to-subject and therefor flash-to-subject distance with a short lens, you get very LARGE drop-off in flash power due to something called the inverse square law. Working from a longer distance,with a longer macro lens like a 150 to 200mm macro lens, keeps your flash output more manageable with many flashes. I vastly prefer working with a 180mm macro at 18 inches instead of with a 60mm macro lens at three inches. With the longer 180mm macro and a flash on a bracket, the flash output changes very little when you move back 1 inch....with a 60mm macro, when you move back 1 inch you have a VERY significant loss of light due to the inverse square law. Short macros like 55 and 60mm are great for flat copy work, but are kind of a PITA for insects, small flowers, and stuff like that.
One answer to yo-yoing flash power due to changes in flash-to-subject distance is to have your light held in *one* position off-camera by an assistant, and move the camera back and forth for the right framing. If you don't have an assistant, consider making a sharpened steel spike with grip equipment added to the top,so that you can press it into the ground as a flash-holder; or consider a very small but solid tripod as a light stand/light positioning aid.
I would seriously suggest a good book, like one of John Shaw's three top-selling guidebooks to closeup and nature photography before you sink one or two large into macro gear.