I'll let other people speak to fast roaming. Not my area of expertise. I've never used it because I've never needed it. I've never had a home so large that wasn't well served by one main device. I use my secondary device only as client bridge in my office where it connects to my 5GHz "backbone" with a better connection than any device can get. That is more because my laptop doesn't have AX and it does have gigabit ethernet.
Both of these things are best done manually.
The whole paradigm of band steering is best done by device management. Put devices where high-performance isn't necessary on 2.4GHz. Smart TVs, ROKUs, printers, that sort of thing. They can all be relegated to 2.4GHz. Save 5GHz for the devices that matter, like your laptop you are streaming torrents to.
And I have yet to find an ACS algorithm that works well. One big issue with ACS is that the routers aren't necessarily well placed to see interference that the devices on the periphery can see. Generally a good wi-fi scanning app is your best friend. This way you can roam the peripheries and see what channels may be interfering better than the router can.