Sockets: Always prepare sets of 5? What is the best way?

You mean like how today we marvel at extremely complex networks of analog TAE sockets in every room? Yes, yes, it hasn’t been that long since it was assumed we would need something like that in the future.

Just use deep boxes, then you’re always good.
For horizontal arrangement, always insert the cable entry at a 45-degree angle, so insert it diagonally; then the claws of the sockets cannot damage the cables and the socket base remains free for retrofitting.

How deep exactly are deep boxes?
So if I have a 3-gang box, do I, for example, go in at 45° on the left side, connect all the sockets, and then go out again at 45° on the right side?

A bit off-topic, but can someone recommend an online shop where I can get good cables for private use? For example, I need a conduit for concrete and don’t necessarily require a Franconian conduit that is coated inside and halogen-free. A cheap conduit is sufficient here. In other words, good quality but not too expensive because it’s for personal use.