Nice Shifu ,your sauerkraut looks great.
The amount of salt is in almost all recepy's different BUT never under 10gr/kg we added no water ,the fluid is pure nature
Further there are many ways people make it,I think almost all will work,golden rule work clean.
What I do is the first week,every day force a stick from top to bottom of the jar on at least 4 places swirl only the stick around a little,this helps to release gasses and avoid bitternes,this is done in Germany and balkan countrys so it must be tried and proven.
Some people keep it for a year easy,and it is still good.
Ok you freeze it,in that case the sauerness will not change anymore.
When you keep it in jars or a big sauerkraut barrel after a week or two .....it goes on fermenting slowly and will make more acid,but limited.
In my country they used to have natural sauerkraut and a spiced version,the last one is hard to get,as younger people hate to bite on a pepper corn,so the complaining people won this battle
But now we have our own.