2. Sorting threads by number of merits the OP has received.
This would create an inbalance making it difficult for lower ranked members to get publicity for their post, so if for example, they wanted to notify others about a potential scam, their post would be buried below other posts even as soon as it is posted. I do not think this would be helpful in any way.
It is just a sorting function, so it's up to the user, they can sort by 'new' or for times when they just want to surf some 'good' threads, they can do so by 'sorted by merit recieved' function. I don't see how it would create imbalance.
4. Getting notified when some one quotes our replies.
Already have a bot created by a user name piggy.
A native feature. I have been on several other forums, alert thing for new quotes/replies/mentions keeps discussions flowing.