Does it spawn automatically, requires any other plugins, does it have to be Halloween?

You have to set halloween.scarecrowpopulation to a positive number (it's the population per km²)

You don't have to do halloween.enabled for it to work (so you don't have to enable related events).

Sorry very new, do I put the halloween.scarecrowpopulation in my server.cfg or is it in the plugin file

Yes exactly, in the server.cfg.

Would this be the command"halloween.scarecrowpopulation 1"(or any positive number)I am very much a noob

You can add a line like this:

scarecrowpopulation "10"

Thanks very much for your help

No problem ;)