PH newbie and big machine / before maiden

Hello to all !

Even if already discussed somewhere I’d like to ask a question that seems very important to me.

I am going to maiden a big x8. TOW around 15 kg.

specs :

Foxtech D130 X8
KDE 5215 (435 kV) motors with triple blade 17" props
Herkules III okto XL ESC board (400 Hz, also set in PH)
Pixhawk 2 on copter 3.5 rc5
mission planner latest beta

motor min/max pwm according to manufacturer set to 1100-1900
everything calibrated
modes preset are stabilize, alt hold and loiter on 3pos switch
rate roll/pitch kP on poti ch6, ( limits set to 0.08/0.2 )
in extended tuning ALL values default (4.500 … 0.135 … etc)
Throttle mid is on learn and save ( however that exactly works, could find precise description (for a newbie to PH ))
data log is extended to IMU also for the vibration issues

And now my question :

One of my buddies (flying similar machines) told me to simply lift off with all values on default. It should fly.
But being new to pixhawk I would like to run autotune when everything seems ok. Is there any risk on this
concerning that we are talking about a big bird ? Or should I preset some filters / values on which I don’t have
enough experience yet ?

And should I, prior to flying, set the (separate) level in acc calibration ?

Any hint could be very helpful and is very much appreciated.

Many thanks in advance,