Hardware recommendation for HA, NodeRed, NAS

Hi,

currently I am using a Raspberry Pi4 running NodeRed, Kodi, PiHole and a Samba-Server with an external SSD. This setup works just fine and has enough power for everything I have done so far. Now I also want to implement Home Assistant to get a prettier Dashboard, since I don’t like the look of the NodeRed Dashboard. My first idea was to just install it on the same Raspberry Pi, but I think it gets to messy with all these things running on the same device. I don’t want to have too many devices, but I want to split it up to multiple devices and am not sure what makes the most sense.
I also have an unused Raspberry Pi 3B+, but I read multiple times, that it might not be powerful enough for Home Assistant in the long run - what is so demanding with HA?

How would you split up these systems? Have seprate devices for everything?
Or a separate NAS + one device for NodeRed/HomeAssistant + one device for Kodi/PiHole?
Or just one more powerful PC like an Intel NUC for everything?

Linux server + docker

You can have multiple HA containers or single HA with different views

All this can be done on RasPi to test and moved to other hardware in future
RasPi is fine until you get into video things like image processing or camera. RasPi 2/3 are slow but not terribly so. Never used RasPi 4