I am creating a PostGIS 2.X data base to store some 500 or so sites as points in it, which are distributed in the northeastern part of Germany, northern Poland and parts of the southern Baltic coast. I will also store some lines and polygons from the same in it, which will be needed to calculate distances and areas. In general an error of about 10-20 m would be acceptable for my task.
I was thinking of storing the spatial data as geography in ETRS89 Lat/Lon (EPSG 4258), which should allow for best compatibility over the entire area, but cost me some functionality compared to geometry. Since I am new to PostGIS, I don't know how strongly this will affect me.
So here are my to questions: 1) Is there a considerable downside to using lat/lon-data and geography for this task? 2) Is there a projected SRS I could use for this area without getting to much of an error to my measurements?