I’ve had two 2 tap towers on top of my keezer for a year now with no reinforcement and it’s been fine. Not sure how much heavier a 3 tap tower would be, but if I were you I would think about reinforcing it. Even though mine are fine without, I remember being 50/50 about reinforcing it when I was building it - it seemed to me to be at the limit of what it could bear for my 2 tap towers, so I reckon a 3tap tower might push it over the edge.
As far as cooling the tower goes, I wouldn’t bother. I live in Australia and haven’t felt the need to cool mine. The first pour is slightly foamy, but not enough for me to care about. I know a lot of other folks do cool them, though - probably lots of DIY designs on the net...