When creating a new post in those sections, select the checkbox to 'Set Thread Status Is WikiPost'.
It's on the todo list to create official wiki posts... feel free to go ahead and do so though.
You're talking about your signature, right? Signature limits for greenies are 250 characters and 5 lines.
Edit: limit for greenies has been increased to 1000 characters and 15 lines.
Multi-quote is supported. Highlight text and then click reply button. Highlight more text, hit reply again... Or am I not understanding the problem correctly?