New topic, piggyback or add to older post


Hello all I have a couple of questions as after years of learning what I read , recent joining of forum, and finally after all my time collecting , asking questions. Most of my questions over the years have been answer after enjoyably searching. But I have a few ?'s that I cannot find basic answers to.
#1- If another member posts new topic and I have something similar but was not covered in their topic or other topics that I looked over. Do I jump on his/her topic and ask mine? Is that hijacking? Or accepted?
#2- If I see another older topic that I can add thoughts on or have questions do I post there?
#3- if I post new topic to me , is it acceptable to only post one reply of gratitude ,say a week after created to avoid clutter. What is respected and acceptable?
#4- New topic and multiple questions for it . Should I give all the info that I believe is correct and ask all questions or start new topic?
#5- When there is conflicting information, do I refer back to older topics or archives? Is that rude to members that are participating in topic?