No idea on the hacking. Most of the beeping are safety features which can be turned off, but it's less beeping and more a quick chirpy to alert the driver to a change in speed limit or upcoming speed camera.
In terms of data collection don't live in the US? The only secure way way to block it is remove internet access which doesn't exactly help: the information on the modification will likely lead to insurers refusing cover and warranties being voided.
Pretty sure truenas scale can host everything you want so you might only want one server. Use Epyc for the pcie lanes, and a fractal design r7 XL and you could even escape needing a rack mount if you wanted. Use a pcie to m.2 adapter and you could easily host apps on them on a mirrored pool and use a special vdev to speed up the HDD storage pool
The role of the proxmox server would essentially be filled by apps and/or VM you could turn on or off as needed.