If you can't host the map, try checking if its over 8 MB in file size, because the maximum multiplayer limit for WarCraft III maps is 8 MB.
As for posting the maps you can just attach the files to your post, just scroll down in when you're posting, and under "Attach Files", select the "Manage Attachments" button. A window will appear, then click "Choose File" and browse for your map and press the "Upload" button.
Otherwise you can just upload the map to Hive's map section but that should only be for finished maps rather than incomplete maps, or just upload the map at a file sharing site and link it to us.