you're talking of technical aspect of multi-gig and I'm looking at economical.
I'm talking about both. The total "cost" includes not just dollars and cents that leave your pocket but also overhead in choosing (or not choosing) the best setup for your needs. This may, or may not, be another all-in-one, which is fine either way.
I don't want to change my hardware every time something new happens or there's going to be some speed boost.
Ironically enough, that is
precisely the point of deploying discrete components instead of an an all-in-one. Every time some new feature paradigm rolls around, you
don't have to go gutting your entire network stack to accommodate for it. Wireless standard changes? Just replace your APs only. Needs more switching capacity and/or port speed? Just replace your managed switch(es). Need to go from 1Gb to multi-gig routing? Just replace your router. With a full swap of one all-in-one for the next, you're unseating your entire network stack all in one-go. I guess that could be viewed as a perceived benefit if the momentary inconvenience of having to reconfigure everything trumps the need to setup and manage discrete pieces. But for the performance and stability of a network overall, I'd argue a single point of failure like that would be more disruptive. Nevertheless, I digress, and we'll probably just have to agree to disagree on that point, at least for this setup, which is again completely fine.
As I hinted before, I certainly get the impulse to keep everything simplified into a one box. And we must account for the Polish market -- not everything is as available or as cheap as it may be in the USA. So my suggestion of that switch, or any switch for that matter, may be moot. Considering those items plus your stance overall, I'm actually going to reverse course here and say you might as well give the GT-AX11000 a shot. It's clearly the route you're desiring to go. If it falls short at any of its roles, you can always re-purpose it as just an AP, just a wired router, etc., then slot in other components to fill those needs. Perhaps that's the best approach right there -- start with the all-in-one, re-purpose and add gear only if necessary.
