The pull-up resistors on the 7809 gates are basically for speed I think - TTL chips can't pull up very hard,
but a low value 470 ohm resistor on an open collector wlll provide more pull up current for faster switching.
The better solution would be to use 74HC chips, not old TTL.
The diode in C2 means the gate will discharge fast (so the MOSFET switches off in time, ie before its
counterpart starts to conduct - this is to prevent shoot-through which would destroy all the MOSFETs).
C10 decouples the power rail to reduce EMI being radiated from it. It will probably need a good ripple current
and ESR rating to avoid overheating.
C4/R34 protects the current sensing chip from undervoltage spikes induced from the large dI/dt on the main
MOSFETs. With lots of current being switched really fast, significant voltage spikes are induced on nearby
wiring. The fact that the current sense wire is grounded by 0.1 ohms will do nothing to protect against
magnetically induced voltages like this, which are created directly on the wiring itself.