I see that I can post new topics, but are there any limits on what type of topics I can post, or how long my topics / replies can be?
Types of topics should be consistent with the theme of the board you're posting the thread topic to. Any length is fine, but consider how much information and context people need to understand your topic and respond. Don't "bump" a thread back to the top of the list more than once a day.
Also, as a newbie to this Forum you should read this
Introductory For Newbies thread.
Make your threads and posts constructive. Ask new questions. Start conversations on new topics. If you do this, you'll earn the respect of others.
Good luck and welcome!