Wolfgang, with a 1.15 service factor, [ ie 5,75hp ], often built in by makers, the blowers will still not draw more than your allocated 70A @ 240V. I make it 27x 1,15 = 31,0 AMPS, running each motor = 62,0 AMPS. Starting amps could be reduced by sequential starting of course.
With a 37,5kVA transformer, you will need 13.44 kVA or 36% of its capacity, with 20% more [16.2 kVA = 43%] if starting more than once per hour. Unless reactive load or power factor is mentioned in your contract I think adding capacitance, to bring pf closer to one, is just added expense, for the figures seem to indicate that your equipment will operate well within the specification. I'd guess the poco allocated the 70A limit from motor amperes tables anyway. If I were writing your specification of the supplied equipment, I'd qualify starts per hour, voltage sag limitations, start amps and transformer share limits to protect your position.
Wood work but can't!