There seems to be some confusion here on many levels -
Transparent vs Ooaque
Opaque covers anything, if lighter goes over darker you induce a shift so work light to dark to avoid issues.
Transparents always darken, but they’re see through like candy so use them for tinting and washes, (Transparent's are easier to erase than opaques but that’s another story)
Regarding what colours to buy, as Dave said, depends what you want to paint, but I would suggest the Createx Illustration colour wheel set (or the equivalent in another range). I see no point In Limiting yourself to primary colours when the paint costs less than a bubble tea to purchase.
something else that needs to be understood is that you can’t make any colour with primary paints, this is a myth, you can most certainly mix nearly every colour needed for PhotoRealism, which is usually desaturated pieces. If you draw a line between red/blue and yellow on the colour wheel you can theoretically make any colour inside the triangle but not outside it. I say theoretically because all paints have bias to warm or cooler version of itself, this will effect its ability to make certain tones, ie - a lemon yellow vs a sunset yellow will result in a vastly different spectrum of colours.
This subject fascinates me and I’m happy to answer questions, I’m my class I go over and demonstrate this more than anything, when you understand colour theory the world opens. It’s sooooo simple too, but that doesn’t make it easy to understand, as usual, we humans make it more hard in our own heads