Good day Zhu Li
You find your blowing pressure by finding the pressure where you can keep your bag steady on tone and doing so with steady regular breaths and look at the pressure gauge. We normally do this with drones only and having a chanter bleed plug inserted. It is very easy to hear when you are steady with only drones and the bleed plug simulates the air usage of the chanter without the noise of the chanter.
I make a chanter stock extension with the pressure gauge attached which fits between your chanter and your bag so you are able to see your pressure while you are playing. I make the bleed plugs to suit the exact chanter flow for the piper and with these bleed plugs you can practice your bag technique almost anywhere because the noise level is so low yet the bag is using the same amount of air as it would be with the chanter attached. In your case you will have to rely on your new tutor to help you with this as he will know what to do.
Because synthetic reeds not require require moisture they do not alter in pitch as they get wet from your breath so they do not need to be played in. This is a big advantage for a learner like yourself. There are many that claim the sound of synthetic chanter reeds are off putting but I am not sure it is too much to worry about. In the first World Online Solo Piping Championships, players from different locations used synthetic chanter reeds and were placed as high as 2nd. Maybe the judges were disadvantaged because the events were recorded, I am not sure. Maybe the judges just judged with their ears.
This is a video of Fred Morrison playing Pibroc'h (piobaireachd) in a formal competition with judging.
https://www.youtube.com/watch?v=4a6v7L8EU7EThis video is also Fred Morrison playing for a piping audience in an informal environment.
https://www.youtube.com/watch?v=eQAl7kQpikYIn the first video he is playing up at band pitch, (mid 480's). I believe he is up at this pitch so he is at about the same pitch as the other competitors.
In the second video he is playing a different set of pipes and is pitching in the mid 470's, also very steady.
To my ear, the high pitch is too bright and does not have a good harmonic with the drones whereas the low pitch is not so harsh on my ear and does have a nicer harmonic with the drones.
You decide for yourself but I think the sound speaks for it's self.
As you develop your piping your ear will also develop likes and dislikes. At the end of the day, what your ear likes is probably best and you will enjoy playing alot more if you like the sound you make.
I will get round to making the videos as I previously stated but at the moment things are very busy.
All the best
G