Yes you are allowed to post anything you would want to sell on as many web sites as you like.
You are not limited to one site only.
There are some web sites that are at no cost to you. You would have to google for these sites. In selling your property your self you might would want to check out the For Sale By Owner (FSBO) web sites.
There are many of these webs sites. You would be required to google for these web sites followed by your city and state, also. Though many of these sites might be nation wide, some might have a local web site
I hope this has been of some benefit to you, good luck.
Yes as long as it’s free you can post your property whenever you want.
You can post it on as many as you like. Buy billboard space. Sky write.
Yes you can.