The ordering matters and the post has it right: the pack goes last.
Buying a frameless light pack while still carrying a heavy tent is how people end up miserable, because those packs carry a light load beautifully and a heavy one appallingly. Cut the load first, then the thing that carries it.
The other reason to wait: once shelter and sleep are sorted, the pack you need is a size smaller than the one you would have bought, and volume is the cheapest weight saving there is.