re: aliyah and Eiruv

Question

1) I thought that the shulkhan arukh says that if there are no kohanim then a yisrael should go because of darchei shalom. What would Rav Abadi prefer a levi should go or a yisrael. 2) I was wondering if you can cite for me the sources, or general area, in shulkhan arukh and the Gemara that discuss exactly what can be used as an eiruv (i.e. wall or string).