..would such an addition in my situation be overkill?
IMHO, it would. Just consider how many potters never used one.
Certainly, it will have a positive impact: especially, on more even heat distribution throughout the chamber. So if you have a problem with uneven firing, by all means, try it. Otherwise, I doubt that you'll notice any real difference. But this is just my humble opinion.
No need for the extra holes in the collection cup at all. Make them in a rigid part of the pipeline connecting the collector and your fan. The openings can be easily made adjustable through the use of a hose clamp or a similar device partially covering the holes.
I'd, probably, make the holes closer to the collector just to keep the rest of the line cooler and somewhat less prone to corrosion.