Hmm, you have quite a few questions. I'll try to address each as best I can.
Okay, so it appears your topic was merged into a preexisting one, you can find it here.
- http://mlpforums.com/topic/78322-favorite-anime/page-13#entry2952556
- I couldn't seem to find your second one, but I would assume it has been merged also.
Generally, the moderators notify you when there has been a merge, however I'm not quite sure why this wasn't done in your case. You shouldn't feel discouraged when creating any new topics, just ensure you take a look around the forums for anything which already covers what you want to ask. The moderators merge topics to ensure there aren't two different topics covering the same sort of topic.
There is no way to delete your topic once you are "finished" with it, however you can contact the moderators if you no longer wish users to comment on it, and they will be able to lock it for you.
To create a poll, you click the following "Manage Topic Poll" on your first post to your topic. You can also access it through the "edit" button.
My last point may have been a bit vague, so if you still have any questions I am here to help.
Dovashy's post in my topics have disappeared was marked as the answer