I think it was mentioned in a WOB that Rashek did not actually consume a Lerasium bead, but rather directly used the Well of Ascension to become the strongest allomancer ever existed.
Welcome to 17shard! It's unfortunate that most of the time I am a lurker, and thus I still don't really knew enough about that to help you, but I am pretty sure there are others who could.
Besides that, 来直马来西亚的读者这里再次说声欢迎。