Hi varnguyen!
1. Currently there is no such feature that allows you to make legend position fixed relative to chart parent div. Of course you can still create your custom legend, but then you have to give up on native legend features or implement them yourself.
2. There are few methods that allows you to hide xAxis line, for example setting
lineWidth value to 0.
API reference:
https://api.highcharts.com/highcharts/xAxis.lineWidth
Demo:
https://jsfiddle.net/BlackLabel/Lht7dfuq/
3. When it comes to this question, I'm not quite sure what you want to fix. If you want to adjust format of yAxis.labels you should probably use
format property. Please next time provide me with more specific informations including description of your expected results.
API reference:
https://api.highcharts.com/highcharts/yAxis.labels
Demo:
https://jsfiddle.net/BlackLabel/x8q6vw3j
In case of any further questions feel free to contact us again.
Best regards!