Microcontroller Inputs (Arduino Nano - U5): Inputs to microcontrollers like the Arduino Nano often require pull-up or pull-down resistors to ensure they don't float when not actively driven. If any of the digital or analog pins (D0-D13, A0-A7) intended for input are not connected, they should be defined in the software either to use internal pull-up resistors or connected externally to ensure a known state.

MOSFET Gates (Q1, Q2, Q3, Q4, Q5, Q6): The gates of MOSFETs (pins: G) are high impedance and can float if not connected, potentially leading to unexpected behavior. It is good practice to use pull-down resistors to ensure they remain off when not explicitly driven on. This seems to have been addressed for some through connections to control signals, but any unconnected gates should be considered for pull-down resistors.

Unused Pins of U2, U3, U4 (IR2101): In the context of the IR2101 high and low side driver ICs (U2, U3, U4), it is crucial to ensure that any unused input pins are properly terminated to avoid unintended behavior. For instance, unused IN pins (HIN, LIN) should be tied either to the logic high or low, depending on the desired default state of the outputs.