What are the prescription regarding a bhikkhu or a monastery having a lay-attendant?

I am curious about vinaya regulations & accounts otherwise relevant to a householder's attending to the bhikkhusangha. Of interest are lay attendants in particular, how far one can go in being useful, what makes a good lay-attendant as to ideal & minimal qualification. Not particularly interested in the circumstance of an anagarika or a novice's circumstance, although i would appreciate a delineation of differences very much. References & general thoughts on the matter are welcome.