If you want to use MultiChain to manage a cryptocurrency which is presumably open to the world, you should use the native blockchain currency rather than issued assets. This let you create a fee mechanism by which users have to pay for their transactions. Without this, the chain is totally open to be spammed by anyone at no cost. But there's quite a bit more it it than that, so if you want to create a serious cryptocurrency you should consult with an expert who can help you configure all the parameters correctly.