I've been taking photos professionally for 10 years, so maybe I will be able to help you.
The 5mm LEDs are a good solution on one condition. You need to use lots of them. BY 'lots' I mean enough LEDs to create a 70mm diameter ring without any spacing. You will need to mill or sand the tips of the LEDs in order to avoid any hotspots or color rings. This setup will work. You can make the ring smaller if you use a smaller lens. With macro photography the ring light needs to be as close to the lens as possible. For example using a 77mm ring of LEDs on a 52mm lens will tend to create a strange dark spot in the middle of the photo, when taking shots from short distances.
You can also cut out a rim out of opaque polycarbonate (pelxi or lexan, whetever the name) and glue the LEDs to it. It will diffuse light even further.
But the only concern is light output. It may be insufficient and may need long exposures. If you want to have a high depth of focus you need apertures in the f11-f22 range and this could give you shutter speeds of a few seconds.
You can also use any high power LEDs. The K2 LEDs, whether new or old are really cool. I have a few and they are more than enough for your project. You don't have to buy some P4 or Q or Z-whatever bin because you will be using many of them. In the case of the K2 LEDs you will need to buy 6 or maybe 10 of them and you will have really lots of power. But with just 6 or 10 LEDs you need a diffuser to create a ring of light and not 6 spots of light. And remember that the further the LED is from the diffuser, the more diffused the light is, so you will need to get a PVC tube and build the setup around it.
