If you go with a towbar, I would recommend ReadyBrute towbar with integrated proportional braking. Its the least expensive way to get a towbar and braking system. Lots of satisfied users on RVnet.
BTW: Yes I would recommend towing 4 down. Its just less to deal with, once you pull into the camp ground. You can't always find a pull through site, so trying to push the dolly around and get it out of the way would be a pain at best. I camp at state parks, which often do not have level entrances to the campsite. I can't imagine trying to push a dolly back up into the site, of even leaving it attached to the coach and trying to back into the site, especially if it is dark.