Estimate speed of wind through a hole in a spaceship hull

Your are right, as the air approaches the hole the speed is great enough to change the density, so it is compressible flow. If the hole was a nicely shaped nozzle you would calculate:

$${dot {m}}=C_{d}P_{0}A{sqrt {frac{gamma}{RT_0} left({frac {2}{gamma +1}}right)^{frac {gamma +1}{gamma -1}}}}$$ Where: $dot m$ is the mass flow rate, $C_d$ is the discharge coefficient, $P_0A$ is the product of pressure (away from the hole, called stagnation pressure where the speed is very low) and hole area, $gamma $ is ratio of specific heats (use 1.4 if air at reasonable temperature), $R$ is gas constant for air ($286J/kgcdot K$) and $T_0$ is temperature in Kelvin (Celsius plus 273.15).

The Wikipedia article (https://en.wikipedia.org/wiki/Choked_flow)brings up a fact I had not seen before: flow through a thin oriface does not choke, but I believe the above equation with $C_d$ of 1. would be the limiting amount of flow.