My Pi 3 ran HA “perfectly” for the last 8 years or so. But now the 64-bit requirement is driving me to a Pi 4 or 5. Would love to have the latest for future proofing, I even see NVMe as an option, but I’m also annoyed at having to burn more power and especially to maybe have a fan running just to run the exact same application. What is your advice for hardware, memory, and storage in 2026?
NUC or NUC equivalent.
The price/perf advantages of Pi don’t exist anymore.
If its my personal box… with 2 or more processor cores and 8g of ram or better. My personal HA host has 4cores, 16GB ram and a hallf-TB SSD. I think it was about 200bucks when I bought it. Mem has spiked so it won’t be that cheap now but…
Right now RAM / SSD / NVME will be your limit and highest cost points. For those, id pick larger than min required of course… but personally for storage and ram on any box I build, I crank those as big as my budget will comfortably allow at build time. (why my ha box has 16g/500g) Base specs will be fine for HAOS especially if you’re fine on a Pi3 now but when you get your pretty new fast machine… The temptation to load the apps. 
What kind of apps are you loading on HA? Do you at least install Linux on your NUC?
On a Nuc you have a couple options (cause lets face it smallest nuc is 4x what HA needs)
Remember HAOS IS an operating system unto itself.
HAOS on bare metal - totally acceptable.
My PREFERRED way is HAOS inside a VM on Proxmox.
Apps = New vocabulary for ‘addons’ (because it wasnt complicated enough.)
You can load ‘Apps’ inside a HAOS install - basically specially baked Docker containers specifically for HA…
No they’re not available as standalone docker containers. If you want docker bare - use docker and your favorite container registrar…
Yes it’s a very easy way to run.