I would like to create a map (of a part of the North Sea area of The Netherlands and Germany) with a few labeled markers at specific locations (lon/lat coordinates) in the North Sea. I have a current development version of QGis available; I think this will become 3.0. (I cannot use a released version; this is what I can install on my OS.) The purpose of the map is as an image in a scientific paper, to illustrate the location of some offshore structures relative to the surrounding countries. So the printed size will be 12 cm (hor) by 4 cm (vert), say.
I am a complete beginner using GIS software. I have tried to follow the tutorial at http://www.qgistutorials.com/en/docs/making_a_map.html, but the color was purple and I couldn't manage to set appropriate dimensions. I also had a look at How to create a printable map of labelled markers with OSM background?, but it didn't seem to apply to my QGis install and out-of-date in general. I furthermore tried to download some OSM data as detailed on https://wiki.openstreetmap.org/wiki/QGIS, but no data was actually downloaded because
runtime error: Query ran out of memory in "bbox-query" at line 1. It would need at least 512 MB of RAM to continue..
So I am at a loss as how to continue. A task that I had assumed would be easy (‘just cut out a piece of an existing freely-licensed map, add some markers, done’) turns out to be extremely involved. It is not necessary that QGis is involved, but other GIS software is most likely not available to me. (I previously tried to use Marble for the job, but that didn't work either.)