Fugu caps are made by the user "eat_the_food".
https://geekhack.org/index.php?action=profile;u=53945One of the best artisans, in my humble opinion.
You can find some topics here on Geekhack.
https://geekhack.org/index.php?topic=81390https://geekhack.org/index.php?topic=79513But you have to keep looking for when the GB starts.
Or you could create a topic looking for some1 to sell u a fugu with the colors you want. It's better to wait.
You don't have to necessarily use the fugu, look for other artisans as well.
If jelly keycaps were made with cherry profile it would be awesome with your set, for example.
...do you think blue legends on the blue keys (ESC and arrows), or purple as on the purple ones?
Normally, it's better when the legends of a group of keys have the same color as the caps of another group.
Like black caps with orange legends in one group, orange caps with black legends in another group. (Carbon set)
It's a easy combination that works well in the vast mojorities of sets.
In this case, since it would be hard to use purple legends on black caps, could be better to combine the color legend with the color of the cap itself. In this case, purple caps with purple legends and blue caps with blue legends. Actually, the blue caps could have black legends, so they can match with the black caps. I think it's better this way.
(Another option for the theorical idea would be the black caps with cyan legends instead of purple).
At the end, I will have to use the most used phrase: "it's your KB so it depends more of your taste".
Sorry for the cliché, but it's true.
I think that even if the led direction is not optimal, will still be better than black legends on black caps.
That much is obvious, but I understand your concern.