ABN, GST and registered companies?

Hi. I'm relatively new at this. I've been fortunate in getting quite a few exhibitions, solo and group, but I'm still struggling with some things. For example, I'm not sure if I should be applying for an ABN, registering for GST, and/or registering as a company. At the moment I'm just trying to do business as me. I'd appreciate any tips people might be able to provide. Thanks.