Originally, there is a fairly big difference in the source of information the speaker is using. However, it is also true that many speakers do not follow this.
～～（の）よう = your own judgement expressed euphemistically
～～らしい = you heard something from someone or read about it somewhere.
Your sentence 3b and 6a are incorrect. Drop the な.
5a and 5b are incorrect. Change the で to another particle. I won't explain it here because I just did so yesterday in the following thread:
http://www.japanforum.com/forum/japa...eech-help.html
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テロが起きて = terrorism occured (and)
で言ってたけど = (someone) said in (the weather forecast) that