Your comment made me think of this video: https://www.youtube.com/watch?v=rQDdmobnGcw I don’t know if it really fits your case, but the general message of men oftentimes not learning to keep up social relationships and that it sometimes huts them in the long run might be something to be aware of :)
Well, in German we say “bitte” or “gern geschehen”, which is close to the “welcome”. Of course, people can and do also say “kein Problem”. I guess in my experience it depends on how I feel about the task and the person I did it for.