Question Question about cumulative GN for all strobes combined

[Luko]

Here is my question: If I add the YS-03 to my system (probably mounted on an arm off of the cold shoe mount on my camera where the focus light is often mounted), I will have 3 strobes each at a Guide Number of 20 for a total of 60. Would this give me a similar amount of light as a pair of strobes each rated at GN30?

Strobe power is not the only criteria that should be taken into acount.
If you're doing macro then power is NOT a criteria - almost not at all- at the extreme end, when you snoot your subjects you will only use one strobe with minimum light.
Power becomes a requirement when you're shooting wide angle, but then the other most important criteria is COVERAGE, you don't want a hot spot in your pic and fall off all around. This is why you need wider diffusing strobes equipped with light diffusers or better, domes, to get a more even light on a larger area. Your S2000 are very much conceived for macro and focused lighting. Hence if you're asking for more power that means you are aiming to shoot Wide angle.
Then No brainer switch your S2000 to more powerful Inon 330, S&S YS D3 (I have some reservations with this brand following what happened with the YS D2) or second hand Retras if you can find them (would be my prefered choice. (Disclaimer I own 2 original Retras, I was using before a pair of Inon 240).