First fermentation under pressure. Every tips appreciated

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Jul 26, 2020
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I'm sure theres answears to all of my conserns in the forum, but there is simply to much for me to digest and I can't find information that apply to my conserns 100%.
I made a batch of a dark lager (for christmas) a few days ago. Decided to split the batch into one plastic vessel and one 24L corny-keg which i mounted a spunding valve to. I mounted a dip-tube-lid to be able to get clearer beer from the start, I figured there will be a massive amount of yeast in the bottom of the keg.
I started the fermentation of both the keg and the plastic vessel in a 10-12°C room. Left the spunding valv almost open to keep it close to atmosphere-pressure. After the fermentation has speeded up a bit I moved the corny-keg to room-temperature (20°C). I closed the valve to raise the pressure....But... I'm not sure at which pressure I'm supposed to keep it. My idea is to keep it at about 30 psi until the fermentation is ready, then move it to 1°C for conditioning. To keep a good carbonation-level I want to lower the pressure to about 10 psi in the fridge which I think would match with 30 psi @ 20°C. Will the pressure be lower once the beer gets colder so I don't actually should change the pressure right away? Or is it better to release gas to 10 psi before I chill the keg? I'm not familiar with the laws of physics here. What I mean, Will the beer be severyly over-carbonated if I leave the high pressure in the keg? Or will the pressure decrease simply by the colder temperature? If this is the case, I don't want to release the gas and get a severely undercarbonated beer.
How about the process overall? Any suggestions?