Powering Arduino + Other 5V Hardware with a single 7.4v LIPO battery

I have some questions about powering my Arduino Mega and other 5v hardware with a single LIPO battery.

My battery is a 2200mAh / 2S1P / 7.4v / 2Cell.

I’m using a step down regulator (Pololu Step-Down Voltage Regulator D15V70F5S3) with this battery to power several 5V devices: 32x8 LED Matrix, 2xNeoPixel Rings, 2x30mm fans, LED chaser.

I also have a LIPO low voltage alarm not present in this diagram which will alert if any cell drops below 3.3v.

When supplying the Arduino itself with power should I have a wired connection directly from the battery to the Arduino, which bypasses the step down regulator?

Should I use a barrel jack to connect the battery to the Arduino or connect to the VIN pin. Is the benefit of connecting to the VIN pin, that the battery will last longer since excess voltage won’t get lost as heat through built in regulator on Arduino?

A 7.4V Lipo battery is 6.0 to 8.4V. That 6.0 is too low for an Arduino, but if you limit it to 3.3 per cell, the 6.6V to VIN might work (barely).

The difference between the power jack and VIN is a diode. There is a diode from the power jack to VIN, and then from VIN into the voltage regulator to 5V.