I make a smoothie with banana, frozen bluberries, frozen mango chunks and water. I sometimes further enhance this by adding fresh juice of half a lime or lemon. It's about 4 cups that will usually last a day or two.

Can I add natural vitamin C like amla, rosehip and acerola powder into this smoothie? Will this be more synergistic?

Can I also add other herbs I take like gotu kola, nettle leaf, astralagus & ashwaghanda(I already mixed these two)?

I am guessing maybe it’s OK because none of those fruits has enough protein or fat to interfere with herbs – am I right?

I just want to simplify my regimen.

Without protein and oils there will not be any significant absorption issues.  Although if you are going to mix the herbs you need to add them right before you drink the smoothie.  If you add them when you make the smoothie then store the smoothie  the moisture will lead to oxidation of the nutrients and some other compounds in the herbs.  The less time the herbs spend in liquid the better.