Go in peace. God's servants are not "directors of conscience", but ministers of His Word. To have sanctioned it would have recognized idolatry. To have forbidden it would have put Naaman under a yoke to Elisha. It was for Naaman to decide whether he could do this thing, and be at "peace".
a little way. A phrase found only here and Gen_35:16 with Gen_48:7. = a stone's throw.