It is always good to start with a latest version, but as i understand - you are also new to docker as well. So i would suggest to complete the tutorial using Alfresco 5.2 + SDK 3.0.1 version first (as explained in the tutorial) and then you can start exploring Alfresco 6.x and SDK 4.0 later. Generating the sample project structure will be same for SDK 4.0 as well, which you can do later and try to apply the concepts you learned so far.
Main concepts are going to be the same on every version, so once you are comfortable - it will be easy for you down the line anyway. The tutorial is really good so follow along.
Same hands on code reference is also available using SDK 4.0 for Alfresco 6.x. See here (You can also refer these at a later point of time):
You can read Deploying and Running Alfresco Content Services 6.0 to understand how alfresco 6 is used with docker. Its a good read.
(ACSCE, AWS SAA, Azure Admin)