Yes, there are many bounty campaigns not accepting newbie users, especially for signature and Content bounties, but most social media campaigns are accepting newbies. You can pay a small fee to get the Copper member rank, which is considered by most campaigns as a Junior member, and it will allow you to join many campaigns.
Yes copper member is very effective to increase rank so it is equal to Member. But it must also be balanced with the quality of posts and activeness in this forum.
Regarding the limitations in joining bounties, everything is clearly written in the rules of each bounty. The key is to read and understand it well. As far as I know, the most effective and profitable cryptocurrency forum is this forum. Another alternative is to be able to join bounty portals such as Bounty hive, Bounty0x, etc.