This is my second ever PCB. I am trying to integrate it into a preexisting 12V electronic car. The idea is to take all the inputs from the JST connectors (stop and drive are buttons, ultrasonic and RFM too) and determine whether or not to flip the relay, which is either opening or closing the drive signal (replacing the digital gas pedal on the car). It is a four layer PCB with the stackup sig/gnd/pwr/sig, with small traces and all the communication on the first layer and longer digital traces on the fourth layer. Any advice on slight improvements or significant issues? As you can probably tell, I'm a beginner so any assistance would be super helpful.
USB to Serial Converter Ch340C 12VDC to 5DVC AP63205WU-7 5DV to 3V3 MIC23050-SYML ATMega328P 5V to 3V3 Logic Level Converter SN74AXC4T774 RFM69HCW datasheet RFM69HCW hookup guide (used to determine connections)