when can you consider yourself successful in opening a thread? I think when it makes it past one page
You’re right but dont forget there’s different types of thread. There’s your regular thread on one topic that posters reply to. For this type of thread to get past say 30-40 posts is a good achievement. So eg Boro Park Eruv (221 posts), finding the right seminary (214 posts) are great threads.
Then you have feeder threads where posts are all on the same topic but do not follow on from each other and posters often revive them from their posting history after long gaps. These threads include eg jokes (769 posts/16 pages), humorous items (which has almost 2000 posts and 39 pages!), word chain game Nov 4th (1329 posts), riddle (1838), limericks (11 pages), riddles (1838), mazeltov (388), things kids said/did etc etc.
On a thread of 1-liners like ?? ?????? ???? ????, for me the milestone is more the 21 pages than the large amount of posts. So Well Done deiyezooger!