ERA5-Land Hourly Precipitation Chart and Map

Question

I am little bit confused how to handle the "ERA5-Land Hourly"-Dataset in GEE. I want the total precipitation of every month from 2018 till end of 2021 for my area. For the chart I took the reducer ee.Reducer.Sum() because I thought it fits the total precipitaion, but I am not sure if its right.

Besides I am wondering about the mapping. I want to show in the map how the precipitaion went in the last years. Do I take the reducer.Sum() or better the Median?

I also need help with the scale. The resolution for ERA is 30km, but the pixels in the scale 30000 were too big (my region is a small town in Germany) so I changed it to 3000, but I don't know if its suitable. How do I choose the scale? Does it always depends on the resolution?

('geometry' and 'table' are my own assets and not shareable. The are is called 'Kirchhundern' in Germany)

https://code.earthengine.google.com/?scriptPath=users%2Flaraemsinghoff%2FStart%3AKlima

Map.centerObject(table);

var starting = '2018-03-01';
var ending = '2021-10-01';

var Precipitation = function(img){
  var bands = img.select('total_precipitation').clip(geometry);
  return bands.rename('Precipitaion')
  .copyProperties(img,['system:time_start','system:time_end']);
};

var eraPrec = ee.ImageCollection("ECMWF/ERA5_LAND/MONTHLY")
.filterDate(starting , ending)
.filterBounds(geometry)
.map(Precipitation);

print(eraPrec);
  
print(
  ui.Chart.image.series(eraPrec, table, ee.Reducer.sum(), 10000, 'system:time_start')
  .setChartType('ColumnChart')
  .setOptions({
    title: 'Precipitaion (ERA-5 Monthly)' + ' ' + starting,
    vAxis: {title: 'm'},
    hAxis: {title: 'Date'},
    series: {0: {color: 'blue'}}
  })
);

//ERA map
var ERA = eraPrec.select(['Precipitaion']);
var ERAsum = ERA.median();
var pal = ['#FF0000', '#FFA500', '#FFFF00', '#00FF00', '#008000','#008080', '#1E90FF', '#0000FF', '#000080']


 Map.addLayer (
       ERAsum.clip (geometry),
       {min: 0 , max: 0.015, palette: pal },
       'Niederschlag'
       );

//export ERA
 
 var export_map = ERAsum.clip(geometry).select (['Precipitaion']);
 
 Export.image.toDrive ({image: export_map, description: 'ERA_Kirchhundern', scale: 3000});```