Some sort of collection of relevant rules and regulations, or even an article outlining the process of setting up a small business (SaaS, small scale, if it's relevant) in Germany.

For the UK there's pretty good guides online, and gov.uk has some useful information for Britain. But I know (assume?) the process is quite different in Germany.

Subscribe to the Onlinehändler News and maybe Trusted Shops newsletters. They send a lot of spam but also the latest verdicts in law regarding online shops. This is for when your business is already running. Better than nothing.