Never try switching really high currents with a MOSFET directly driven from a logic
chip. You risk destroying the Arduino.
With high power on the output of a MOSFET there is a lot of kick-back through the
drain-gate capacitance when it switches, capable of driving the full output voltage
onto the gate if it isn't driven by a low-impedance driver. This issue gets worse with
higher drain currents and higher drain voltages. I don't know what voltage you are
dealing with, nor can I see if you are planning 50A per package or 50 shared between
4 packages...
The correct way to handle high power with a MOSFET is to drive it with a proper
MOSFET driver than can hold its own against the gate-drain capacitance - these
chips can put somewhere between 0.1 and 10A directly into the gate depending on
which one. I've used the MIC4422 before which is available surface mount and DIP,
and is pretty pokey. Remember lots of ceramic decoupling on the MOSFET driver,
essential...
If you drive MOSFET gates in parallel you need to add individual gate resistors or
you risk inter-device oscillation (10 ohms would be fine).
Once you move to using a MOSFET driver you don't need logic-level devices, so the
choice of MOSFETs is much larger. You will need a 12V supply for the driver though.
[ Oh the other, important, point - a driver chip will switch the MOSFET nice and fast
so switching losses are reduced - at 50A switching losses from a sluggish switchover
can totally dominate heat dissipation. The MOSFET may be 0.001 ohm when its properly
on, but if it takes 10us to switch it'll be dissipating high power for a non-trivial fraction
of the time ]