What's important in particular about having those rights at the "beginning" of the Grundgesetz is that the first 20 articles are immutable and cannot be changed unlike the latter parts of the constitution.
This is not true. Only articles 1 and 20 can't be changed. For the rest in between no such guarantee applies and they were changed a few times in the past. Though most likely restricting any of the freedoms severely would be ruled unconstitutional by the very first article.
Of course, the constitution is just a piece of paper, and what's protecting the rights in practice is a political system (especially courts) that tries hard to keep them.
Most of the rights already come pre-holed with exceptions, though. And lots of them contradict each other. There's lots of leeway, to justify a very wide range of policies as different `tradeoffs' between the rights.