Apart of the danger of old enemies sending you taunt messages or some game trader abusing the service to send you annoying spam messages there's nothing to fear I think. In the latter case just leave a message and we'll ban that -_-.

Of course the same basic rules of every forum or communication platform applies here. You shouldn't give out personal info easily. Especially not the kind of infos that could get your game accounts hacked or your bank accounts emptied. If someone sends you links or anything - don't run somethíng you don't know, don't click links that look suspicious. Use common sense, have a good virus killer/trojan scanner installed and you should stay safe. 

To make sure people don't know characters are linked to each other feel free to create several accounts. You just need a different valid email adress for each. Freemailers are allowed as long as there won't be any spam bots abusing these services.

And please don't forget to use a safe password, at best with numbers so your account can't be accessed withour your permission.