1.Of course the achievements are a good idea( clan donates a total of 20000 donates,get a total of 1000 stars in war...reward is distributed equally between members) maybe this one is a little complicated.
2.sometimes you kick people but they just keep requesting to join back each day! a temporarly/permanent ban can help.
3.lets say we have a clan of 40 members,and the clan gets 100 stars(which is a little hard) we get 5% or 10% more loot as reward only if the clan wins i guess.
4. this one is already said before,but a separate chat between leaders and co-leaders is a very good idea.we use kik app in my clan.Cheers