You would only need the precharge resistors for huge capacitors ( I don't see any yet? ). They should only be switched on for a short period of time, not permanently. The ON time can be determined by comparing battery-voltage against capacitor-voltage. When the capacitor is 80-90% full, it is save to close the maincontactors without the risk of sparking.
You could also use the 'start' function from the original keyswitch to precharge. When you relase the key, you can close the maincontactors.
PS: Yould could install a normally open 'seatswitch' in series to the emergency switch, also a tilt-sensor to cutoff both motors when you fall from the chair while pulling a wheely 
Another good idea is, you have to have a foot on the brake, to close the contactors.
PSS: I don't see a separate arduino-input/switch for the blademotor?