Continuing the discussion from Insteon Hub:
To keep the other thread on topic, I am responding in a new post to your question:
The recommended hardware is at least a raspberry PI 4 which links to one with 4gb of memory in the documentation.
It says a raspberry PI 3 is ok if you have one “lying around”, but as you build it out and add more integrations/addons, it will become noticeably slower.
If you have at least 2gb of ram, and at least the RPI3, and aren’t using it to do anything too crazy (like run an NVR addon or something like that), you should be fine. (There’s some people still using 1gb of ram ok, but they are probably not able to do anything with video) Can i use raspberry pi 4 2gb? - #8 by CaptTom
Using what you have to get going will probably be best to get started before investing more money, but be aware if things are “slow” and glitchy, it becomes tougher to figure out if it is a config issue in Home Assistant or hardware issue. Upgrading hardware will be as simple as setting Home Assistant up on the new machine and copying the config directory (which has all your settings) over. There are a lot of topics on the forum about type of hardware and upgrading if you want to do a search for more info.