I think most brands work - I’ve tried Bloublommetjieskloof products and whatever Organic Zone in Lakeside stocks. I think even normal brands would work. The important thing is to try and keep the amounts low to not shock the system. We don’t need to add as much as the label say - try a quarter of the recommended dose and see how it goes.
I’m not sure about the vinegar. but it sounds like a good idea. Also the vinegar has some carbon in it that will help the soil bugs absorb the nutrients - a good thing. As this post (link below) says, get mulch - anything carbon-ey would work, leaves, wood chips, bark, compost… it conserves moisture and helps buffer against the stuff in the greywater.